We've gone back & forth & back again on this issue as well, Danjo. Same situation... trying to find room we don't have to spare.
We may change this in the future, but what we're thinking of now is a composting toilet hidden behind 'cabinet doors', with a swing-up cover over the top. So closed, it's basically a cabinet face & usable countertop. Open, it's our shitter. No walls to obstruct the view or restrict elbow room. Not big on privacy, but the only ones looking will be our critters, and I kind of get a kick out of seeing the looks on their faces when I out-stink them
No shower, our plan puts that outside.
I am intrigued by your idea. That sounds like it has great promise!