Honestly, I would just be okay with another Battle Revolution. As confusing as the two-player controls were, the game modes in that game were pretty fun. If Nintendo/PTC/GF released a similar game for the NX, that'd be amazing. It'd have a much better resolution, presumably, a far more detailed battle environment, and chances are, more "wacky" game modes to make up for the fact that the main games are 3D and dynamic enough. A new spinoff, as unlikely as it is, would really benefit the series.
On the other hand, I can agree that the Gen6/7 games probably defeat the purpose of a spinoff. If they tried to make another BR/Coliseum/GX, it likely be a full-fledged Pokemon game. Which wouldn't be too bad, either.