Stating the obvious here, but the success of this camera will be largely determined by price. If (as rumored) it's priced in the $1500-1800 region to compete with the D300 and its variants then Canon will sell a bunch of these - not only to xxD owners looking to move up, but to FF owners looking for a second "sports/wildlife" body. If we see a price in the mid $2K's like the 5D2, however, I believe the interest will be much more subdued.
Personally I am unconcerned by high ISO noise (I have a 5D2 for that kind of shooting) and am very intrigued by the possibility of f/8 AF. If the price comes in at the low end I may very well end up getting one of these as a 2nd body.