If you separate the issues of button spacing and button size, it should be fairly easy to prototype a variety of button top diameters by using the mushroom shape used in some of the bigger boxes, either in one piece or by putting a thread on the end of cylindrical buttons which would remove the need for retooling for a new fretboard with bigger button-holes. The Roland button V-accordions have removable/swappable caps as they can be configured to B or C systems - they are all the same diameter and vary in colour and texture. I appreciate that there is not as much wiggle-room on an English and the racket created by catching 2 buttons at once is less pleasant than on an anglo. A further advantage is that melodeon keys give an opportunity to repeat the same note rapidly by using 2 fingers alternately on the same button. I suspect that the English layout is a congenital ergonomic disaster because the thumb-loop and pinkie-plate really limit the options for spacing within the four rows, but I agree that the rows could certainly be separated more widely. There is also the manicure problem - a bit of fingernail makes small buttons easier to use but bigger ones harder.
I'm not sure that I agree with your weight theory though, I reckon that the inertia on an anglo bellows direction change does relate to the weight and can lead to gaps of up to a fortnight between notes with some of the heavier models!
Thanks for the thread

Gaffer