Still, it will easily surpass the Vita in its lifetime.
It will pass the Vita by next christmas, lifetime will be determined by whether the Vita continues to grow in Japan, how long each repective console lasts (my bet is that Vita will last longer) and whether the Wii U has already peaked.
If I had to place a bet, I would put it on the WIi U but I don't think its garunteed. Both systems LT could be 15m-20m.
Well true. If Sony doesn't put out another handheld, and supports the Vita for another 5 years it may pull some numbers just out of sheer length of time on the market. As far as Wii U, Zelda U hasn't dropped yet so I would be surprised if it has hit it's peak. Even if it has, it could easily still sell nearly as many consoles with another $50 price cut and the 2015 lineup. All it really needs to do is keep having these surges of popularity you see from great games which I think we'll see when Splatoon hits, Xenoblade Chronicles X hits, Zelda U hits, and Star Fox hits. And that's if they don't have anything jaw dropping at E3 next year. I wouldn't be surprised to see a small price cut in the summer.