Well the case won't fit anything larger. And that's about 200 watts over what I really HAVE to have. Do you expect more power hungry small form factor cards to come out in the future?
I don't expect the power requirements to go up if the only thing you ever want are those Nano-sized cards that are a relatively new niche. Before the R9 Nano there was really no powerful cards in that size at all
My point is, what if you want a proper-sized card? But I guess that wouldn't fit your case either.