PS4: Get the price under $200, and either add backwards compatibility through some form of black magic or fix PSNow so I can actually play PS3 games on it. Then maybe I'll bite.
XB1: Bundle it with a BJ, sell it for $100 and give me a $150 rebate. Don't skimp on the BJ either, that better be top-notch.
Vita: $150 or less for the portable version, with at least 4 gigs of internal memory (or bundled with a 4 gig card). It also needs some games I'd actually want to play, as I'm hard-pressed to think of games I'd buy for it even if I had one already.
Wii U: Just waiting on Xenoblade X at this point.