I think that you may be able to type faster on keyboards with rather symmetric button movements if you turn the keyboard around 180 degrees. This way, your thumbs can select between more values, on the "number keys".
More generally, is there any evidence that the "home row position" (indices on f and j) is optimal?
I hate to just post conjecture without gathering some experimental data. I hope that I have time to test some of these ideas, albeit informally.
WM