I'm really hoping that Canon will really go out on a limb when they release their competition to the mirrorless wave. Various execs have been quoted on multiple occasions saying things like "small cameras can still have mirrors; we've done small SLRs in the past".
I think they're playing the waiting game as mirrorless sales have impacted their low-margin compact sector a lot more than their high-margin DSLRs, & I think they want to be last to the party & steal the show with the most attractive entry a competitive price point. Knowing that such a thing will likely have to be manufactured at massive scale and make them very close to DSLR-like margin, I think we can rule out a Canonet redux à la Fuji or Leica (the V1 does have a metal body though).
I think it'll come down to whether the thing is designed by focus groups & marketdroids or photographers. Hopefully they really listened to their customers & got a lot of input from CPS members in the early design stages. With materials and manufacturing science what it is today, I don't think that "profitable consumer camera" and "serious professional photographic tool" have to be mutually exclusive. But the design will dictate whether they are able to fulfill that.
I've been going over this in my head for a while now, and in all likelyhood I think we'll end up with something that looks like the bastard child of the Powershot G and modern EOS cameras, hopefully with a little bit of AE1 or F1 DNA thrown in for good measure (or perhaps EOS IX if not, ugh). I believe that they'll stick with the APS-C sensor size just like Samsung & Sony did as they have a lot of R&D invested in their own foundries for it (though I'd be perfectly happy if they used the Super 35 sensor size as in the C300

. The trick will be that they'll design a new DSLR mount specification that will have a registration distance just long enough to fit the smallest APS-C mirror box they can possibly design inside. This is pretty consistent with the adapter patent we've seen floating around.
This will allow the use of all their nice EF telephoto lenses with a small adapter, and also allow them to design new non-retrofocus wide angles for the format (has anyone noticed that the newest non-L/TS-E/macro prime lenses Canon released came out in about 1994?). The smallest APS-C-ish sized frame film SLR was the Oly Pen F & it had a 29mm flange focus distance, so M mount RF lenses probably couldn't be adapted, but at least Canon FD glass could. A mirror box like this would allow for non-retrofocus ~28mm lenses, & modern lenses around this focal length (from 24 to 35mm) available to mere mortals is exactly what is lacking in the current lineup.
Don't ask me about when, but I'd be very surprised if they don't announce something in 2012...