I do still believe that Canon will go mirrorless with their 'normal' SLR's (I expect the 7DII to be the first one -> hybrid VF, stunning video functions, many autofocus points etc.) and they will have an EF mount, otherwise they would kill themselves after building up a lens system for, I don't know, 40 years?! I wouldn't bet on the M system.
What is the point in going mirrorless and keeping the EF mount? I get the lens compatibility, but by keeping the EF mount, you basically limit the size of the camera to, at best, be the size of the SL1. Can't really make it smaller than that, and if you want more processing power (many point AF, etc), it'd have to be bigger.
So, if you're not gaining size, I'm not seeing the point in going mirrorless and EF mount.
Canon may end up making a mirrorless body with built-in speedbooster.
1. They would keep the EF mount and all FF lens support
2. No need for FF sensor, lower price, more sales, more profit
3. No more dust specks, no more sensor cleaning, just think about the level of weather sealing it could have
This is an interesting concept, but, I have to imagine that technologically it'd be pretty complex. And, since those speedboosters all run in the $4-600 range, you're talking a big price addition to any body.
if they implemented that, it'd have to come in a prosumer or higher level body, as they wouldn't be able to price it <$1000 most likely.