But if I want a new engine it is because I want "interesting" things.
What UE4 is at <1 TFlop?
Then that's your issue. Honestly, you're not getting what you saw in that UE4 tech-demo at E3 in either PS4 or Xbox3. That was done on a GTX680. Scaled down version? Sure, why not?
If you really want to see extraordinary graphics using UE4 to its potential, get yourself a PC and hope that Epic pays attention to it. Otherwise, stick to PS4/Xbox3, which won't look terrible, just down-scaled.
Regarding your question about <1 TFLOP: Who knows? We don't know the specs of the GPU in Wii U (though it hints to be 500-650 GFLOPs). Your guess is as good as mine. If you're looking for particles, then it probably can be done on there, considering that Epic said that the interactive particles can be done without any sort of performance hit.
It'll be a scaled down version of whatever you'll see on PS4/XBox3. That's all we know.
So basically you mean
Wii U = Semi Perfect Cell
Durango/Orbis = Perfect Cell
PC Gaming Last Year = Super Perfect Cell
PC Gaming 10 Years Later = Super Vegeto
Fixed for what I believe is more accurate