I'm currently reviewing two EF-M mount lenses from third party manufacturers: Tamron 18-200 VC and Rokinon 12mm f/2. They are both very good lenses: the Tamron does a little bit of everything quite well. But the little Rokinon (manual everything) is a true treat. It is basically a better version of the 14mm f/2.8: less distortion, similar sharpness, and can use traditional filters. I LOVE it! The only thing holding it back is the basic limitations of a crop sensor (as compared to a FF sensor).
My full reviews will be live in the next couple of weeks.
I'm glad to hear of further development for the M. It definitely has limitations, but it produces surprisingly good images. I actually used a 60D for a recent review of a crop sensor lens and was surprised by how much less "clean" the images were compared to the EOS M images. I haven't used a 70D/7DII yet, but I suspect the images from the M will be closer to the 70D than the 60D (I do anticipate the 70D/7DII having the best IQ of the three).
I'm not sure I'd be willing to spring for a MF lens for this camera (esp since I have the most excellent 11-22mm), but I greatly look forward to your review of the Tamron. I guess I'll find out how useful that 1/3 less MFD than the Canon turns out to be.