Never - Xbox One will outsell them both.

See here for full analysis.

http://gamrconnect.vgchartz.com/thread.php?id=183441

Though recent sales make me think it will manage holidays 2015.

I think the PS4 will play more catch up this holiday season as well. Would say when FFXV comes out the PS4 should close in on the Wii U massively

At home console sales numbers in Japan, if it takes off it can happen in 2016, I guess.
If it keeps on outselling it by ~4k/week, instead, it should happen in ~300 weeks, that is in 2020.

Wii U would be dead in Japan and pretty much elsewhere by 2020, so late 2018.

Now seriously, 2016.

Q3 2016 sounds nice

MGSV, persona, kingdom hearts, ff and bloodborne, maybe dragon quest, once they all release then i think it will surpass, so basically late '15

All depends on what games are released. At this point, I see the Wii U maintaining it's lead for quite some time. The lead should also widen by a fair margin for Nintendo beginning next week with SSBU.

If the PS4 passes the Wii U in Japan, I wouldn't expect it to do so until sometime in 2016.

In Japan? Not sure. It's the one market where Nintendo does quite well and the PS4 hasn't really taken off there like it has in the rest of the world. Plus, that market is much more handheld-oriented these days so any traction the PS4 does gain is going to happen very slowly.

If it does overtake the Wii U, I don't think it'll do so for a couple of years.

It really does seem like barring the PS4 starting to sell like the 3DS over there, 2016 is the earliest we'll see it happen. I'm thinking more like 2017, maybe even 2018.