Can Valve do the same with their controller? Release a Windows driver so that I can use it with my emulators?
You may be able to use SC-Controller: https://github.com/C0rn3j/sc-controller
Note: the Windows support is a WIP and the devs don't have the new Steam Controller
You would just need to add your emulators as non-steam games in Steam. Then you get controller support.
You may be able to use SC-Controller: https://github.com/C0rn3j/sc-controller
Note: the Windows support is a WIP and the devs don't have the new Steam Controller