The truth is, after the initial rush, the XO and the PS4 are going to face serious competition from the 360 and PS3, just as those two did from the PS2. I honestly wouldn't worry all that much if they struggled on the front-end, as a lot of games are going to be bi-generational early on. I think they'll really kick it into gear after a revision/price-cut, however, and perform well around the middle of their respective life-cycles. Next generation won't be as big as this gen, though I think Nintendo is going to take a disproportionate amount of that hit.
I believe Microsoft and Sony are going to be in a serious race to see who can cut production costs and be the first to gain a large-scale bump from a price reduction. If they're still struggling after that, then I'll worry.
