Steam works fine on my Gentoo system. For some reason it doesn't detect the S3TC extension on OSS drivers though; but hey, I'm running git versions of almost everything .
Back on topic : I read the post on G+, and as an avid follower of Wayland, I still call bullshit on their reasons. (referenced as on the G+ page) :
1) X is old and crappy to work with. Seems to be the consensus.
2) "We didn't want to use Weston." The reference compositor is reference for a reason. You do your own after that. In fact, rolling your own compositor could help highlight some deficiencies in Wayland.
3) "At the time Mir was started, Wayland's input handling was basically non-existent." So starting from scratch instead of helping out seemed like a good idea... Deep Thought Material.
4) "We need server-side buffer allocation for ARM hardware; for various reasons we want server-side buffer allocation everywhere." Can't comment, no idea there.
5) "We want the minimum possible complexity; we ideally want something tailored exactly to our requirements, with no surplus code." First, this isn't going to happen, a Wayland-like product will eventually grow out of it. Second, if it does happen, you'll be the only users of Mir...
If I'm wrong somewhere, come at me...
Oh, and I hate blueberries