I had it as a mind game for a while to design keyboard layouts that would be optimal for Swedish, German and English (my main languages). I found that you can only get so far with algorithmic approaches. I liked the ones I designed without computer help much better than the one i made with generic algorithms or machine learning, despite being worse on paper. Neither "combos" or distance travelled explained what made the layouts good.

Now, I never used any of the layouts for more than a month or two, but it was still a fun experiment.

I will admit, I type exclusively on 40% keyboards. I used to have a Happy Hacking Keyboard, (in fact, the original Happy Hacking Keyboard (HHKB) with separate PS/2, Sun and ADB cables, still have the board and cables), then the HHKB USB, then the HHKB 2. One day I saw a 40%, in fact an original "minivan" by "The Van Keyboards" and thought I would give it a shot. For someone who uses the computer all day, this was an advancement over the HHKB in the same way the HHKB was an advancement over the 104:

* Your hands move a lot less during typing.

* Your hand is much (_much_) closer to the mouse to grab it.

Even though there is a slight learning curve using layers, after a short while it becomes just like the muscle reflex for "hit shift to use the alphanumerics", etc. When I have to run into the data center or go somewhere and use a "real" keyboard for a moment, I am reminded of just what a huge time difference it is to grab the mouse, or reach for keys like PGUP/PGDWN, etc. It may not be for everyone, but I advocate for giving small keyboards (even split ones) a try.