I don't really see a point in maintaining z80 compatibility, considering it would be illegal to include an 84+ emu anyways (unless it had kOS on it)
It's not illegal if it ships without a ROM (or with kOS, of course) and you have to provide your own, I think.
Also the emu doesn't have to come with the calc. It can be separate.
And yeah I agree the focus should be put on one calc. Since uberspire is working on Ubercalc, let's focus on OTZ80 next Summer so more energy can be put in it.