Interesting points, Lalop!

Indeed, on a normal keyboard you should count this as same-finger for the poor pinky, to show how much trouble it's in. In the case of many layouts though, it might be an idea to measure efficiency both with and without symbols! In my head, you can use one letter-block layout and another symbol-block mapping if you want to – for instance, keeping the Swedish symbol key mappings and special letters while switching the main letter block to Colemak! Or a Wide mod, which affects the pinky a lot but should be assessed independently from the layout itself for the most part. That also makes comparisons between keyboard models easier.

I remember getting in some pain with a book on Amphetype, as it had many quotes. That led to a steady stream of this kind of thing:

"What were you thinking?"
"I don't know!"

Note the ugly dance the pinky has to do between those lines, typing four symbols in one string (and all but one of them shifted, to boot!).

I tried to train myself to use Caps+Space more for those line breaks, but it didn't always come automatically when going for speed. Also, since the left pinky is needed for Shift immediately before and after the line break, using Extend isn't smooth in that particular situation.

I have no really good solution for this problem, I think.

Indeed, as Davkol points out it can be even worse on an ISO board. One solution is a Wide/Angle mod, so both shifts and Return are close to your home position and the pinky gets less overload.

I would suggest using ring-pinky-ring too. Especially if this is a combination that you have to face frequently, then you must get started with it without delay.

I mean you will only get used to it with time. I started touch-typing on qwerty on normal mode but then have gone on to make slight variations in my "standard touch typing" regime to accommodate for certain difficult word combinations on qwerty. Now, I can juggle them up depending on the word, and I constantly work at such combinations too. Believe me, it doesn't take much time to get used to. The conscious mental effort in the first couple of months is all that matters.