It's not great. It's only good for staunch advocates who refuse to run any other operating system. Linux still isn't good enough for joe sixpack to run it as a daily driver. Until they get joe sixpack on board, it'll forever be a niche product without enough inroads to support a gaming ecosystem. (...) OS X has more of a chance at becoming a capable gaming OS than Linux does, and that's really saying something.
Except for cost. That's what powered the Android drive, it wasn't the technical superiority. There's probably more people gaming on phones and tablets than any other platform when you count Angry Birds, Candy Crush and such. Chromebooks running on Linux also seem to sell reasonably well for the same reason. If Valve can get a a range of steamboxes out there to sell to everything from a $99 box to sell freemium + $1-5 games to a $999 gaming rig to people who don't really care about having a desktop anymore with their tablet/convertible covering those needs there's probably a market for gaming boxes.
It does of course assume that you commit enough to get it off the ground. Nobody wanted to code for Android either before it got popular. And if Valve is backing off now that the Microsoft Store doesn't seem that big a threat after all, it might take many years. But Linux is well propped up by servers, supercomputers, embedded, cell phones, tables, chromebooks... it's not going away. Particularly not in the direction we're going with more cloud, less local it's certainly not going to get worse.
The driving force behind Mesa is Intel, they're certainly not going away. Pretty soon they'll hit the big OpenGL 4.0 and it seems almost all the prerequisities for 4.1 and 4.2 are done once they get over that hurdle. And they certainly want to keep their OpenGL ES current if they want to play in the x86 smartphone/tablet market. AMD also apparently like their open source driver for embedded/custom projects, less legal hurdles for customers who want full control. So maybe they don't win, but I don't see how they could lose much terrain either.