I can see Tekken coming to Switch.  They did put Tekken Tag 2 on Wii U.  Granted it was a late port but it did grace the Wii U.

We do know it is coming.  It isn't hard to envision what next year might be like as these games finish being prepared for port or getting further into their development cycle.

If Street Fighter II & ARMS do well than I can see other devs being on board with porting fighting games to Switch. It could potentially be a very good fighting system

Street Fighter

ARMS

Smash Bros

Pokken Tournament

Tekken

Marvel vs Capcom

Injustice

Didn't realize I put Switch in there instead of Wii U but I'm sure you realized my mistake.  The three I bolded seem like good predictions on what might come on Switch for fighting genre.  Smash is a given and I expect them to announce a possible Smash Deluxe a la Kart Deluxe during E3 or something like that.  Just include all that expensive DLC that Smash had and put a few more stages, items and modes.

I wonder if Nintendo will develop any of their own games using Unreal Engine 4?

interesting question indeed

It would save them having to create their own engine, plus a Nintendo game would no doubt look great in that engine.

I think they won't, maybe save from a few minor titles, it's great that UE4 works well on Switch but it's not an engine customized specifically to work on the Switch, hence probably not allowing as much as the latter could . But I could see Nintendo starting off from UE4 to create custom engines specifically for the games they want to make...

I feel like this deserves a thread of its own. It's truly incredible how we're at a point where a mobile form factor device such as the Switch can run something like this. (at 1080p too as they said if a few adjustments are made).

No wonder it's getting a lot of UE4 games. It's been known for a while that the Switch is capable of a lot (despite some dumb comments people will try to make acting like they built the machine themselves and know better than anyone else) and this only just further proves it. 

And it's not like anyone can say this isn't Switch footage when it was stated that this tech demo was specifically made ON the Switch. 

Switch has full support from Khronos. So Open GL 4.5 and Vulkan as well.