Now keep in mind, this is from not yet playing a character on the PTR:
I do not believe that IV will create a new raiding spec outside of specific fire-resist/immune fights (see: Al'ar and part of Illidan, etc). I think that 10/48/3 (and according to various theorycrafting sites as well), will still be the #1 damage spec. Now with this in mind, it will boost damage all around no matter the spec, but I think that giving up the deep fire points will hurt more than help.
In PvP I think that it will do a very good job, it will most definitely help in arenas, I can't see why it wouldn't.