There will be a separate patch, FOV just applies the cosmetic changes for the most part.
I've noticed a few gameplay changes as well as the cosmetic stuff: notably that it's no longer impossibly difficult (well, for those of us who are rubbish at combat) and a few tweaks such as being locked out of the Williams quest until the appropriate part of the game; also one or two places that may be new, though it may simply be that I never noticed them first time round.
So I am curious as to what I'm missing out on, but since I've just asked the same thing in another topic on the DKS subforum maybe I shouldn't be prattling away about it here too...