I personally don't think the pros are worth the cons, but then I'm one of those AltGr aficionados. I'd rather swap AltGr and RShift as Pieter suggests, myself (but I won't).

How about a dual role for the space bar?

I actually tried the dual-use space bar configuration for a short time. I find that it didn't work very well once you started typing at a reasonable speed.

Agree, the solution is definitely more thumb options - shorter and split space bar. I have a keyboard that has a split space bar and I use the left half as a shift key and it works really well.  The problem arises though when I'm not using my usual keyboard, e.g. when I'm on my laptop. Then I have to revert to the normal shift key, which is very unpleasant once you have gotten used to a thumb key.  Hence this OP was really about trying to find a nice solution for standard keyboards.

I've actually been practicing typing this way for several months. I call it AltShifting. I wanted to test it myself before encouraging others to try it. Here are some things to consider:

• The position of the AltGr is very important, otherwise your thumb is forced in really odd positions for an extended period of time. You want to thumb to rest naturally on the key.

• Right Alt is generally the closest key available next to the obtuse spacebar, but its position isn't standardized. Some foreign keyboards have smaller spacebars that make it more accessible (especially Japanese keyboards). Most keyboards have it too far right for standard layouts.

• Wide layout mods fix this problem (those that shift the resting position of the right hand one key to the right on the home row). With these the thumb rests naturally on the Right Alt key, as long as your wrists have proper posture (spread to align with your arms, rather than bent to be pependilar to the keyboard).

So I've exclusively used wide layouts to test this shifting method on my Microsoft Reclusa, modified to swap Shift and AltGr functionality using Microsoft Keyboard Layout Creator 1.4. Here are my experiences. I'll try be thorough.

Cons:

• Because I used Microsoft Keyboard Layout Creator, the space key doesn't work while holding down Right Alt. Considering space ends sentences and shift begins them, this can make the timing for AltShifting less forgiving than it could be. Backspace and Enter are affected the same way. This method does not change the functionality of Right Alt or Shift for shortcuts (you may prefer this)

.

• On top of that, using your thumbs will throw off your timing for shifting. I forgot how tricky shifting was to learn when I was a kid. HOld SHift too long and you'll capitalize too much. let go too soon an you've missed it. You might need to pause after AltShifting a character to prevent errors. Eventually you  get the timing down and your typing speeds will be back to normal.

• Pressing the spacebar with the right thumb is less comfortable. Those who exclusively press space with their left thumb like me will be unaffected by this.

• Same hand shifts are uncomfortable. Having only one shift key makes it a necessity for right hand keys. Keys closer to Right Alt are more awkward to press together with it, especially those on the bottom row which necessitate a pinching posture. On the opposite end, the number row is harder for the right hand to reach while shifting.

Pros:

• Greatly reduces load on the pinkies. Shift is the fourth most common key on the keyboard. The right thumb handles the extra load just fine. When keeping proper wrist posture the shift keys an uncomfortable stretch for the short pinkies. This can be reduced my moving the whole arm down for it, but moving the hands off the home row can be slow and confusing. By avoiding this, AltShifting promotes better typing posture.

• It's easier to learn from scratch, since it's one button. No need to juggle between two shift buttons.

• Reduces same finger typing and row jumping a little bit. For example, when typing "Mac" in standard QWERTY or Colemak, shifting with a pinky opposite to "m" leads to a same finger use for the following "a." This is true for capitalizing many words whose second letter is pressed by a pinky, as long as the first letter is on the opposite hand (e.g. has, have, many, may, lastly, make, yay). Colemak's use of "o" on the right pinky makes the problem even worse than QWERTY (e.g. for, so, may, today, would, some, most, good), but AltShifting eliminates this downside.

• MAKES CAPITALIZING WHOLE STRINGS OF LETTERS A BREEZE, SO CAPS LOCK CAN BE FORGOTTEN.

• Having the Shift keys act as AltGr makes the layer more accessible, especially for the right hand. Holding Shift + AltGr allows another layer if you need it.

Ideas to improve the experience:

• Fix AltGr disabling common functions when held down (such as Space, Backspace, Enter).

• Disable Right Alt shortcuts (but keep Left Alt functionality).

• Use "Sticky Keys" to simplify timing and reduce errors. This accessibility feature in Windows and OS X allows "the user to press and release a modifier key, such as Shift, Ctrl, Alt, or the Windows key, and have it remain active until any other key is pressed." It's basically how shift works on smartphones. This could also make the keys near Right Alt easier to AltShift, turning the combination into more of an upward roll than an uncomfortable pinch.

• Use a layout whose frequency of shifted keys favors the left hand to reduce same hand shifting. For shifted letters, QWERTY and Colemak have 59% on their left hand, Workman has 56%, and Dvorak is abysmal with only 34% on the left hand. Colemak Mod-DH Wide is the best available option.

• Design a new layout that with this in mind. I've been working on an optimized layout one for half a year now that has 64% of shifted keys on the left. It's codenamed "Butter." Like AltShifting it aims to be an ergonomic solution for standard keyboards. I'll probably make a thread on it sometime soon because I would love your feedback.

• Modify the keyboard to make Right Alt easier to press, or import a keyboard with more accessible buttons for the right thumb. The JIS standard seems optimal, and can cost less than $30.

• Program the right hand's shift state to be a numberpad, eliminating the downside of being unable to AltShift the right half of the number row easily. In fact, this is a much more ergonomic way to type the numbers, eliminating the need for a numberpad on your keyboard. It's so nice to not have to reach for the numberpad and number row anymore.

• Now that you can shift state a "virtual" number pad, get a keyboard without one. While this obviously saves deskspace, it's biggest benefit is making the mouse easier to use with a keyboard. To keep your keyboard centered many people use the mouse far to the right of their desk. The excessive reaching for it is not ideal, nor is having to move you're hand all the way over there and back every time you switch between the mouse and keyboard. Close that gap.

• Don't AltShift with QWERTY. Learn it only for an alternate layout. Learning a new layout can make you unlearn a previous layout, right? Well this is such a radical change that it's also like learning a new layout...and if you're using two layouts it's like learning two extra. You're better off saving the muscle memory for standard shifting for the standard layout, think of it as your plan B in you have to use a keyboard without your preferences. I am able to switch between AltShifting on my ergonomic layout and standard typing on QWERTY without any issues.

Maybe the AltGr key could be a dead key? Meaning:

1. Press AltGr
2. Release the key
3. Press any letter and it get's shifted. 

So: AltGr, release, m ==>  M   

That way you don't have to hold your hands in weird positions. AltGr could then even keep it's normal AltGr function when held down.
For instance:  AltGr, hold down, press e, release keys  => é

What if you want to type several letters in Caps? Well: either CapsLock, or the normal Shift key.

I'd glad my input could be of use. Thanks for the feedback. You guys make some good points.

@pieter

Sticky Keys adds this functionality. I'd been trying it out today and find it more comfortable so far. As a plus, holding it down to capitalize a string of letters still works this way.

That's a clever alternative to further reduce pinky usage. Any idea on how we could make it work?

@stevep99

I'd agree that overall it's clearly an improvement, as long as you use a wide layout that isn't Dvorak. I just want to emphasize that it's a learning experience w

Autohotkey would probably solve the issues I'm having.

I was targeting people on this board with that suggestion, who I assume are using an alternate layout or are planning to. This is like learning a new layout, and in my experiences it's difficult to be proficient with more than two layouts at a time. You mentioned this issue earlier:

"I have a keyboard that has a split space bar and I use the left half as a shift key and it works really well.  The problem arises though when I'm not using my usual keyboard, e.g. when I'm on my laptop. Then I have to revert to the normal shift key, which is very unpleasant once you have gotten used to a thumb key."

QWERTY users can definitely benefit from this quality of life change, but it has a bigger learning curve than any comparable change (wide mod, backspace to caps lock, etc.).

If you are AltShifting with a wide layout mod on an ANSI keyboard (which we tend to use in America), you'll lose access to several symbol keys that would have been on your right. This is my resulting wide layout:

Same-hand AltShifting the parentheses is also uncomfortable. This is why I find "Shift-AltGr switch" an important compliment to AltShifting. But I'm probably biased by my custom layout. Without it, you could use the standard shift keys to do parenthesis and such, so it could be functional. You may shift the layout over one without making it wide to allow extra punctuation keys on the left pinky, as Colemak Mod-DH suggests:

I didn't have any issues switching over. Relearning shift timing was far more jarring. I feel like you might as well learn both changes together, but I do agree it's not necessary now that I've thought it over. ISO keyboard users may have no issues, and shifting the home row right might fix things for ANSI users.

Eliminating the need to use the hard-to-reach number row is also great plus to me. Ideally I want to fit as much keyboard functionality near the home row as possible. It'd be nice to have an extra layer for navigation buttons. Fortunately, AltShifting opens up the left and right shift keys to be used for separate layers. I dream of comfortably using a keyboard as minimal as this one day:

Yes, that keyboard would be great. Is that just a render and not a real keyboard?  If it were real I would want one - or at least, if there were an ISO version. As well as being portable, it has two extra keys either side of space bar which are perfect thumb keys for the two most important and frequent modifiers - Shift and Extend!

It's a mockup I did in Photoshop based on the Vortex Pok3r keyboard. I removed the top row and shrunk the spacebar to add extra thumb keys on each side. The original is a "60% keyboard layout" and the mockup is close to a "40% keyboard," though you'll notice that 40% keyboards usually remove two columns for the right pinky so it rests on the Enter key. This might make sense for QWERTY, but it's incompatible with alternate layouts that actually use that home row position, and it's incompatible with wide mods. I'd like to make a keyboard that finds some middle ground.

There is a black ISO Pok3r, but it doesn't have the thumb keys I added. The extra long shift keys wouldn't be necessary in an optimal keyboard. A lot of 40% keyboards have smaller shift keys.