Well, most of it is speculation right now (as far as I know)
But the R34 M-specNUr was the last GTR to be released untill 2004. The 2004 will be the next car to be badged GTR and
could be called the R35 GTR. It's suspension will be much like that of the current M-spec (or so says Ghosn). He also makes it known that it's power will be in excess of 400ps. I think that it will be a car much like the previous GTRs in styling as Ghosn said that "After it's rest, we will be bringing it (the 04 model) back strong" or somthing to that effect
*Edit*
Oh, and there really isn't a law or anythign written saying that Japanese manufacturers can't make a car with more then 280hp, it's more like a gentleman's agreement between them to avoid the muscle car HP wars that wracked the US.