When the Steam Controller dropped, I was pleased to see an official configuration for it from the devs, but that just uses bindings mapped to keyboard and mouse inputs. This will allow other controllers to join the fun!
I'll definitely try this on release with a 360 controller, and I'm interested to see if native controller support will make the Steam Controller config work more naturally. Ultimately, I feel I'll probably stick to Steam Controller for about half of my playing and keyboard/mouse for the other half. But...