To be honest, an endless runner Sonic is not a bad idea provided they add variety and numerous stages (not levels per se, obviously, but stages with different themes). Is this going to be like Temple Run? Obviously fitting, but they should also consider something in the veins of Jetpack Joyride. Perhaps a mix of 2D and 3D elements (like the recent Sonic games) would be best.
All that said, it is a bit frustrating we haven't had a real Sonic title (bar the invisible entry that was Sonic 4 II) since Generations. Sega should fix that, and take the chance to put the franchise in order, now that it doesn't have as much of a controversially bad reputation as a few years ago.