One of my current projects is a keyboard. I liked the idea behind the mitosis keyboard, but I wanted a number row and wanted the wireless to use BLE and not a proprietary protocol. I wanted something I could connect to any computer, tablet, phone. I also wanted to add a trackpoint. In addition, I didn't like the thumb cluster.
In order to get the layout correct, I used a keyboard layout editor and designed the keyboard the way I wanted it, with a comfortable thumb cluster, and the correct number of keys. I tested this with the precision method of taping keys to a paper and seeing how comfortable it was.