Cynical Prediction Time!



It's a client that will be forced to run whenever their games are started on your PC. Maybe not their already-released games, but definitely going forward.



It will also be used to "subscribe" to mods like with Steam Workshop.



At some point in the future, only mods that go through this system will be allowed to alter the games. This will be justified by the argument that "players get the same experience across consoles and PC", and that it stops "pirated" or "copyright infringing" free versions of paid mods to protect users and creators.