It seems that the competition between PS4 and WiiU in Japan has been way closer than anyone expected. With the home console market not doing that well in Japan compared to the rest of the world, Nintendo has kept a decent lead over the PS4. Although the gap has been getting shorter and shorter, it seems that has not been enough. WIth 2016  getting a massive PS4 lineup and the NX glooming in the distance, will the PS4 outsell the WiiU before the NX is released? Or will the WiiU keep enough steam to stay on top until its successor arrives?

Is only a matter of time. The PlayStation 4 is in every country the number 1 worldwide (UK and USA too), 100 % next year in japan then > wiiu. In 2016 January to March the PS4 gets more than 25 games in Japan (ign.com = source) and the wii u, maybe 6 ? Later in the year the biggest JRPGs Persona 5 and Final Fantasy 15. Also: The next year is the biggest year for the console in japan, i think. 

Nearly 2:1 in 2015 isn't "close". The only reason you may be fooled to think that is that we're (unfortunately) talking about small numbers all around when compared to healthier markets. (Just as an example, PS4 is #1 home console of Japan in 2015 with almost double the sales of #2, the Wii U, yet in almost 12 months it has sold 400k less than what PS4 sold in the US in November alone).
It'll happen before NX. The gap this year is almost 600k in favor of PS4. There is around 700k left I think? In 2016 the gap will be even bigger.

No. The NX won't launch before 2017, so Wii U will stay strong in 2016 and 2017.

If it has the games that japanse folks like why not

Considering it launches in 2016, I think it may or may not, but in case it does, it won't be by a lot.

No matter what happends in 2016 (nx launch or not) I think the PS4 overtakes the Wii U.

Depends on when the NX is launching...

but I think the PS4 can overtake the Wii U sometime in 2016

If the NX launches in 2016...than maybe, maybe not...if the NX launches later, then yes.

The Wii U wasn't strong in 2013, 2014 or 2014. 

Ps4 in 2014 beat it's 2013 and ps4 in 2015 beat wii u 2014 by a lot.  

Even if you just take this year and not launch aligned ps4 beat the Wii U by a huge percentage.  You're confused because we're currently going through the last 3 weeks of sales where Nintendo always gets the biggest boost because parents are buying it for their kids.  

First half of this year was domination by ps4,  first half of 2016 will be no different.  

Even if the Wii U stays ahead by a nose doesn't mean it held off the ps4 because the ps4 has outsold it every year since release.