FWIW, the ROM of at least one of the keyboards has been dumped, but per my understanding of the forum rules, we can't really talk about that here.

MESS emulates both the Mac and Plus keyboard as an 8021 (implementation here)

I personally only have the original keyboard, although I'm trying to acquire a Plus version (by like 20x for all the compacts I got a while back). But it could be an interesting project to try to build a new keyboard using the same controller...