@ ~17:30 in the GN video "the controller acts as a trackpad and keyboard without Steam running". It appears to not support DInput or XInput so any emulators or other storefront game would need to be manually added to Steam to be able to use this. Such a shame, for me this went from instant purchase to let me get some TMR replacements for Dualsense. I hope they can change this in the future.
Valve has made its $99 Steam Controller official with an actual release date and early reviews have started coming in. Gamers Nexus has tested various aspects of the controller and found it to be quite impressive.