There aren't enough keys on a full keyboard for all the key-bind shortcuts on PC, how on Earth would this work on an Xbox pad? It only has... um... 14 buttons? Our pad is in the cupboard so I can't see it from here. Definitely not enough buttons though. This isn't the most concerning factor however:
How would Workshop content work? Or wouldn't it? I mean for something like a straight up multiplayer shooter like Call of Warfare, Modern Tank World 7 (heh) where there's no 67 million modifications and custom assets it's quite easy to stretch over all the platforms, but when your game has an existing user base who all love the Steam Workshop, the editing tools, the endless clicking to place a tree in just the right place... I just don't see how it would work to be honest.