My idea is for a "modular" controller.
so you would have a bunch of modules (joysticks, buttons etc) all communicating with each other somehow, and then a player could customise their controller layout to their liking.
also, is the transmitter is a module, they can play xbox, playstation, wii U pro, PC etc on the same controller they made, just by changing the transmitter. The thinking behind this is you do a lot of controller mods (single handed etc) and this would mean the person can easily make a single-handed controller, or an arcade-style deck, or a xbox-like layout, and then play their games on all consoles with it.