If what I have read is correct, a drawback for me is the lack of 1080/50/60p video. It looks like a fantastic camera and the adapter is half the price of the metabones smart adapter for the E-Mount. Plus the lenses are build for that crop factor.
From real work experiences of people here (in Japan) with these types of camera...they stick on one lense, fit all the accessories they can and that's it. I get some "nerd!" looks when I switch between my 19mm and 50mm prime. Would love to put the 70-200 F2.8 Canon lense on my 5N body...
Hopefully Canon won't fudge this mirrorless compact like Fuji did with the X-Pro 1.
Competition is good, so hopefully it'll speed up Sony releasing more E-Mount lenses.
Once it's released, I'll have a play in the Canon shop here.