I have an EOS M, I bought it pre-firesale, and I love it. I previously had a G12, then a m43, neither one of them gave the quality I wanted, until I tried the M.
One small potential improvement to the "M2" which I haven't heard anyone mention should be a simple one - the addition of a bit of a grip on the right front of the camera, would make it much
easier to hold. Even with a pancake lens (22mm) it would not make that depth dimension any larger, but would give you a great ergonomic addition.
The Panasonic Lumix GX7 is a very similarly sized m43 ILC and it has the grip - you can see from a top view photo such as this one, how it adds very little to the size, but it would help you hold the camera without squeezing it, because it gives your fingers a purchase point.
I will probably not upgrade either way, but this is something I would love for them to "upgrade" on the EOS M2.