I don't know if something similar has already been requested and i obviously don't know if it even possible to do but it would be really great to have some "simple" Button-Remapping application.
Take Mario Kart 8 for example. If you're using the Gamepad or a Pro Gamepad you'll notice that the original Button Layout wasted so many opportunities to be much better.
For example: In the original Button Layout you accelerate with "A" and brake with the "B" button. This gets pretty tedious if you want to brake during drifts and you need to "fat Thumb" both Keys all the time.
Nintendo really fucked that up by wasting Buttons by having "odd" mappings like "use Item" on both L and ZL, which is a shame since one of the buttons could be brake (B) instead which would make everything so much better.
It would be great having a tool which you fire up before starting a game to swap Buttons (having Profiles for each game and player would be the next Step, maybe even Launching the Game from Within the app?).
It doesn't need to be too complicated (i know that might sound silly considering how hard it might be to realize) just for example swap "A" with "L" or "B" with "Z".
That way even Wiimotes could work much better for Mario Kart (with the original Layout there isn't even a Brake button) or other games.