reasonable enough educated guess. 4-6 Gb is my own expectation. I'm giving a bit larger of a multiple gen over gen for 1 reason: this was the longest gen ever by a couple years. had new hardware been released at the typical release schedule your 4 Gb would have been perfect. as it stands i think they'll beat that by a bit.
as cobretti mentioned...nintendo dedicated 1 full Gb to their OS which is gigantic. Right now the ps3 OS takes 50 Mb and i guarantee it gets larger but 1 full gig is beyond my expectations. ~0.5 a gig?
so by my expectations we're talking wiiU's 1 Gb to MSony's 3.5 to 5.5Gb for games. now get announcing hardware MSony.