The thing is I don't think anyone cares to try even if there was an engine port. And I'm not sure that is even whats going on here ... "engine port" I wonder how much customization they have to create themselves ... UE4 is highly scalable you build a game for anything and then adjust here and there until it can run on other hardware... but as far as compiling it for use on the Wii U... I bet they'll have to handle that on their own.
Well, the entire engine is open-source, so you can compile the engine for any platform, and make any changes to enable any platform that you want.
In general, I think they'll probably take what's already been done for the mobile platforms, and port that over to Vita and Wii U, as it seems like the straightest shot. I imagine they'll just have to turn some post-processing effects down or lower the resolution, which is all very easy to do in UE4. In fact, there's even drop-downs in the editor for "mobile quality" or "console/desktop quality".
As far as I know, the only reason Epic hasn't done the Wii U and Vita ports is simply a numbers issue: those two platforms have so few users that it wasn't financially in their best interests to port it. But it's an open-source engine... eventually, someone was going to do it.
edit:
Also, isn't this a 2D game? Yeah, I wouldn't really worry about the Wii U or Vita then.
edit 2:
My mistake: it's 2.5D. I still don't really see a problem.