But nothing is technically stopping UE4 from running on the Wii U, it is more than capable of running it if it wanted to. Given that it was designed to run on an iPhone if necessary, running on the Wii U should be no issues with some scale backs.
As for this specific instance- again, the tech demo looks good as a tech demo. This would be the worst art style for a Zelda game yet, so I would hope Nintendo, even if they decided to use UE4 for their next game for whatever reason, actually brought in their signature art style with them. Something like the E3 tech demo would be amazing.
That was my point, it is more than capable enough of running UE4, I was more meaning the porting process would be a lot more painful getting onto WiiU than the other 2 8th gen platforms.
And whatever engine Ninty use, they can take their artstyle with them, the engine is unlikely to define that, it would only define technical limitations.
So exactly how pared back would UE4 have to be before it ran on Wuu?
And that, my good sir, I cannot answer as I have no idea, and it would depend highly on both the game and the talent of the team. There are currently no UE4 Wii U games to judge it either.
If I was to give a blanket generic answer, I would say draw distance, and texture resolution would be the biggest things to suffer.