I know that there's a Linux driver to use the Steam Controller without Steam that is coded in Python, and the integrations API is Python based, but integrations are for adding game stores, not actual functionality, right? Maybe the developers can take that Linux driver and integrate it with the actual program?

Yes, I know I can just launch a game through Steam and the controller SHOULD work (it doesn't always, but that's a different thing), but you can only launch one game on one system that way. I have GOG versions of some games specifically so I can hand a friend my spare laptop and we can play together when they're over, and I VERY much prefer the Steam Controller over pretty much any other input method, so being able to use the controller without having to launch a game through Steam would be great.