To be fair, Vega is supposed to bring further improvements to efficiency and will also use HBM2 to help lower power draw slightly.No its pretty impossible at this point for AMD to compete with the TXP. Even a 5000 shader core polaris would match a 1080 at best.
It would take a seriously power hungry card to come anywhere near the TXP.
I wouldn't say it's impossible for AMD to compete with Titan X at all, they'll just have to really solidly deliver with Vega. In terms of doing better than that? That's more debatable. But I still think a bigger Nvidia card is theoretically not out of the question. Nothing about Pascal suggests it is not possible. Not to say that it'll happen, just talking theoretically.