Why not have the bearings in the forks themselves with through-axles? Given that we're moving away from QRs to through-axles - partly driven by the torque needs of disc brakes, why not follow the natural progression and move the wheel bearings from the hub to the forks themselves.

Generally you want bearings as close to the load as possible. Having them in the fork is as close as one could hope. It'd also allow the axle to be very thick, which would add strength. 

Given that every idea in bicycling has been tried at least once, has this been done before? What are the demerits of such an idea?
Interesting idea but the front axle (whether is be a 15mm through-axle or a 9mm QR axle) does not rotate, the hub-body and by extension the rest of the wheel rotates about the axel via the bearings. Making such a system where the axel does rotate (e.g. unicycle fork) would require creating a capture system (which is the current function of the QR) to secure the wheel to the fork that would likely be less user-friendly that the quick-release based systems we have come to expect.