Most likely, I doubt Epic would show something that is not. I also agree about the official reveal.
Someone in the comments (on the link you posted) made an interesting point: Nintendo should show a new game using UE4, but before showing a trailer, don't say it is UE4. People think it will look alright but nothing special. If Nintendo later tells us it's UE4, after the trailer, peoples minds will explode, lol.
I think Nintendo could win a LOT by showing us a UE4 game. Like, gaining a lot of respect and new potential buyers.
But at the same time, I have low hopes for UE4 to come to the Wii U. It is said that it could only run on very high-end PCs, but then again, a dev which I can't remember said the Wii U could run like a high-end PC.
No sig.