I agree, but... designing one, two, even more entire keyboards is probably easier than designing a good flexible system of modules. It only becomes a total effort savings if you get lots of buy-in from others. The idea is definitely appealing to the programmer in me, though (make the most generic/flexible/composable design possible).

I actually made some single-switch PCBs with some (IMHO) clever design ideas to make one-off keyboards much easier to solder together, but never went much further with the idea.