I like your thinking and so would a lot of others, but Canon probably won't go there -do I remember an interview where a representative from Canon actually said that people that wanted this from a camera should buy a Leica?!
I am really hoping for a mirrorless FF camera. Whoever gets there first with decent primes will earn my money. The Fuji xpro is still APS-C after all.
Why buy new primes? With a FF mirrorless, you can re-use all the old and cheap FD-Lenses. They are much smaller than the EF ones, the aperture is manually controllable, manual focus is much better and the optical quality of the primes hasn't changed much since then...
On all EOS cameras, they can't focus to infinite. Not even with the smallest adapter. That's the main reason why nobody uses them anymore, and why they're so cheap. Shouldn't be a problem anymore on a mirrorless with a much shorter distance to the sensor.