I love the M, but wish it had the articulating a flip out LCD display, a headphone jack, audio meters on all the time, larger battery, side door for battery and SD card, not the current bottom door. HD 1080p60. Use the full frame capture for HD 1080p without line skipping. Eliminate aliasing and moire. Better low light/available light performance without digital noise. Option to record ProRes 10bit 4.2.2 Built in ND filters. Zoom lens with constant f/2.8. A smooth rocker switch in an easy location for motorized zooming like their high end lenses for video cameras usually have. EF lens mount instead of the EFM. Just make the body a little bit bigger for this EF mount and larger battery with a side door. Continuous non stop recording for video to fill the whole SD card no matter what size card we use.
Probably higher costs for all of this, but I would pay extra for all those features if they compete with BMPCC and the GH3 around $1000 or less. I got my M with 22mm lens for $300 and the 18-55mmm EFM lens for $135. Extra batteries with chargers were also very low cost. A lot of quality there for a very low price, IMO.