Not sure how Valve 'pioneered DRM', not to mention that DRM on Steam is purely optional, as in it's up to the game publishers to decide if they want to use DRM.

Unfortunately it seems only indie game developers are opting for DRM free releases on Steam, but again it is the choice of the publisher, not Valve.

As for SteamOS, as far as I've gathered the OS itself will be fully open sourced, the Steam service application will remain proprietary.