I do a lot of wildlife photography and lugging gear around especially on aeroplanes is a problem. I have several L lenses from 70-200 f2.8 IS to the 500mm F4. I normally have these attached to my 1D MkIV. I have often wished I had another short lens attached to a body for quick access but the additional weight was prohibitive.
Naturally when the EOS-M came onto the market I was very excited as I thought this would be a great 2nd and 3rd camera! Lightweight and cheap. Well since then I have been reading all the reviews on the slow AF I put that idea on hold, game and birds don't wait for slow AF may as well do a lens change if that's the case. It seems as if Canon is actually incapable of doing an upgrade as I am sure they would have done so long ago. I guess waiting for Firmware upgrade is a waste of time. I think they may be able to address the problem with the MkII, well maybe.
FWIW, we have an EOS M and a Fuji X100s (and a 1D Mark II if we need to look serious). Frankly, the X100S with it's fancy new focus system doesn't strike me a much faster then the EOS M with either EF-M or EF lenses. I believe the slow/hunting AF reports are exaggerated. If you're really interested in the camera, I'd recommend testing it out before you dismiss it based on reviews. I have little doubt that the next version of the EOS M will be improved in all aspects, but jumping to the much adored X100S, makes me realized how capable the EOS M is. Plus, with that 22mm lens, you're getting some stellar IQ in a tiny, tiny package that you can take damn near anywhere. It sounds like the new SL1 is pretty peppy when not using Live View. It might be one to consider.