The only reason to buy this EOS-M2 (and the future EOS-M3) is the seamless integration of current EF/EF-S lenses.
+10. Some of the M4/3 models are looking mighty tempting. However, my 5D3 with a small prime lens and without the battery pack is "small enough" for most of my uses. I don't put cameras in my pockets.
As a system (or a camera) in own right, the EOS-M/M2 is nearly four years behind micro-4/3. By the time Canon gets to where mirrorless systems are today (e.g. Panasonic GX7 and Olympus E-M1), even Sony will have (in all probability) a fairly decent set of (native, FF mirrorless) lenses.
I think you're being overly pessimistic. Canon could make up the entire 4-year lag in the next one or two models, for example introducing a couple models comparable to the GX7, except that one is FF. The question is whether they want to.