The sensor is still the one thing that bugs me the most. It's not even m43 sized. It's TINY. If Canon were able to do this with an APSC sensor it would be an incredibly impressive camera.
Even better if they were to put it into a weatherproof, drop-proof and water-resistant body. Now, that would be something I'd seriously look into.
1D iii (x2), 1DS iii (x3), 6D, 16-35L ii, 24-105L, 70-200L IS ii, 24/3.5 TS-E, 40/2.8 STM, 50/2.5, 100/2.8L IS, 135/2L, 300/2.8L, 500/4L IS, 430EX II, EF 1.4x ii, EF 2x iii