Upload & Sell: On
Basically a 2" diameter x 1" long heavy duty alloy tube with some plates on each end to support the lens-mounting flange, etc. The tube would surround the Cmos sensor when it retracts into the camera body for new mirrorless DX lenses. Conversely, the tube/flange assembly would extend out from the camera body about an inch to accommodate legacy DX lenses(& legacy FX also maybe!). Shouldn't be that expensive... Just brain storming here...
It's never that easy, though
1" is pretty deep, first of all. It's actually deeper than the entire NEX body at that point - and you still need room for a PCB, LCD, buttons, chassis, etc. So I don't think it's feasible to do in one solid piece. Doing it in 2 pieces might work, but then you have this slider mechanism that has to support a lot of weight and a bending force, which is exactly the kind of force a 2-piece sliding tube is going to be bad at supporting. So it's gotta be a really nicely designed tube, with some pretty substantial reenforcements and a locking mechanism. It needs the mount interface on the front, so you have to create secure electrical paths that will survive repeated extensions/contractions. And since it has to have the mount interface on the end of it, if you break it/bend it/whatever, your camera becomes useless - you can't just discard it or buy a new one. Unless, of course, they make it a modular piece - which is even MORE expensive.
All of this to avoid machining a simple, solid aluminum adapter... But I think we've drifted topics here.