As someone with both a 54 key (6x4) and a 15x5 uniboard, I personally think a 16-18x5 would have a lot more buy in/universal appeal. Having the extra keys mean that people who need the extra keys aren’t discouraged, while those who dont can disable the keys they dont want. You get a similar amount of “split” by having
Another thing is splay and stagger are very personal choices which everyone have different preferences. I think if you are planning to support 2 options, a 36-42 key for the hardcore users, and a ortholinear as a gateway drug for everyone else.