I have this crazy idea, inspired by the interchangeable prism on my LX. I only have the FA1 that came with it but have always thought it was cool.
So here is my plan. Make a DSLR with a normal but removable prism OVF. Also make an EVF with the same form factor that can be swapped in. Sell kits with one or the other, or both.
When the camera body detects the EVF, it locks up the mirror and goes into live view mode. You can choose between the rear screen and EVF as per usual with a MILC. Best of both worlds, yippee!
What can go wrong? Modern DSLRs pack a lot of electronics into the prism, including the light meter. In an LX that lives at the bottom of the mirror box. That space is used by the AF gear in a DSLR. Might be doable, but the light meter would be duplicated in the EVF and OVF, driving up costs.
Another flaw is the number of contacts needed. It could be a great many, making the connection complicated and fragile. Perhaps some sort of near fields comms between viewfinder and body could keep this in check, but this is uncharted territory. R&D could be a big effort.
I am releasing this as a royalty free idea. No guarantee, but since is free it is great value for money.
What say you?