A patent that seems to show a switch that will move a camera from mirorrless to DSLR mode has been published.
Keith over at Northlight provided the animation above and this explanation:
Short back focus lenses such as EF-M allow you to put the sensor much closer to the lens, reducing body depth. However, unless you choose an EVF, there is no way to get a good optical reflex viewfinder. The patent allows you to swap between a focus screen or sensor close up to the lens.
Perhaps a bit clearer to see in this animation of the short backfocus reflex viewfinder design. The sensor is red and the focus screen green (other moving part is a mirror) This allows a reflex optical viewfinder to be used with any short backfocus lens.
A very interesting concept indeed.