A lot of the games that Valve sells as "runs natively on Linux", actually is just a Windows game in a proprietary wrapper for Linux.
Valve has made the decision some time ago to stop marketing games for "Linux", but instead market them for "SteamOS". They are also removing the Tux logos everywhere and replacing them with the SteamOS logos.
That said, they do want to shift to SteamOS as main platform on November 15th 2015, and since I doubt that many commercial games are going to develop a native Linux version, it's quite possible in my opinion that Valve equips SteamOS with a commercial/proprietary wrapper to make it run Windows games, while studios migrate to engines that are also natively Linux-compatible. Even EA is now working on native Linux versions of even their most successful franchise Need for Speed, so apart from the dissident Ubisoft and Microsoft, native linux versions might be available sooner than expected. That's not necessarily a good thing though, who wants DRM on their naturally DRM-free Linux install...
Which leads us to kvm to run SteamOS, which is high performance and doesn't need passthrough with KMS drivers, and the KMS drivers (apart from nVidia of course) are evolving quickly and AMD is also moving towards open source kernel modules for Catalyst, which would give these drivers the same functionality as KMS drivers.
The biggest grow market in gaming is not PC gaming by far, and thus the traditional marketing model of PC gaming is not valid any more. Strangely enough, the advancement of console and mobile gaming vis-à-vis PC gaming might greatly benefit the software on PC's and make PC's better for everyone again, instead of just for shareholders of some big corporations. The best thing that ever happened to PC's and PC gaming might just be that Intel wants to make Intel products relevant on mobile devices, where Microsoft software is almost absent (with actually less market share for Microsoft in the mobile market than GNU/Linux market share in the US in the PC market. The strange thing there is that the US has the lowest market penetration of Microsoft software in the mobile market, even though they used to be the largest back in the Compaq iPaq days... in Europe, Microsoft has the best market share in the mobile market, up to 17% in some countries like France, but the worst in the PC market, whereas in the US, Microsoft almost rules the PC market, but scores really bad in the mobile market, to the point of not being relevant even).
Whatever the outcome will be, I think these are exciting times. The gaming market has been an oligopoly for the longest time now, and there is real opportunity for smaller and new companies now because of the whole situation now. In the end, whatever the gaming platform of choice is or will be, I'm most interested to see innovation in games instead of always the same cold chow of reissues and empty promises and pay-to-play/pay-to-win crap that we've been seeing from the oligopolists in the last couple of years. The games themselves are much more important than the platform. The platform shift is just an ideal opportunity to shake up the gaming world and offer new opportunities for badly needed innovation.