Is it the glorified P&S's canon and nikon and most of the others have released? Or will it follow a similar model to what Sony just released with their FF bodies? Again, what is the identity of mirrorless -- is it a niche fad mid-level attempt to tempt those that favor their cell phones or is it going to be a serious system that pros and enthusiasts will not only see as viable, but want and or shall I go as far as saying - need?
Some people won't like the answer, but here it is:
Professional-level mirror-less cameras have been around since at least the 1930s. For decades, only one manufacturer – Leica – has kept mirror-less alive and then only as a niche market product. Really, nothing of substance has changed. The cameras use electronic sensors instead of film, but all the other relative advantages or disadvantages of the rangefinder versus SLR form factors remain the same.
While a vastly improved electronic viewfinder might make mirror-less more competitive, it would still have huge hurdles to overcome. The mirror-less form factor is great as a light weight street camera, but it offers no advantage for many other applications, such as studio and portrait work. It may even be a disadvantage when using telephotos beyond about 135mm (Notice Leica doesn't even produce any longish telephotos).
So, given that, why should Nikon and Canon rush to produce a professional-level mirror-less camera? Far wiser to let Sony risk their resources on testing the market. If the technology improves and if Sony's sales figures show a true demand, Nikon and Canon can easily enter and very quickly dominate the market. There simply is no good business reason for them to risk their resources on an untested market. Better to let someone else take the risk.
But, I seriously doubt that Nikon and Canon are watching Sony nearly as closely as they are watching Fuji. Looking at the Fuji Pro series, it would be easy to make a case that the future of mirror-less is in the APS-C format, rather than full frame. It offers high image quality while retaining more of the size advantages that mirror-less can offer.
Over at Photorumors, they just published some sales numbers for Japan. For those who dream of a full-frame anything, they are quite eye-opening. Full frame mirror-less constitutes just .5% (that's 1/2 of 1 percent) of the total sales in Japan and in DSLRs, full-frame is just 8.7% of the sales. In short, it is "a small, small world after all" despite the skewed perspective one gets on this and other forums.
Mirror-less may someday displace DSLRs, but only when the technology proves superior, which is far from the case today. If it does eventually happen, it is likely to be a gradual, almost seamless transition, not some jarring "game changing" occurrence.