If Valve can get all new Steam games to run Linux, and eventually all released commercial games follow, it seems likely this will be by far the biggest boost ever to desktop Linux market share.
There are still unfortunately some issues, like the lack of a good 3D API, the closed-source 3D drivers and poorly funded open-source ones, the fragmentation between distributions, and the fact that the only mainstream desktop one, Ubuntu, tends to be divisive and is isolating itself from the biggest contributors.
However, added interest and market share is the fundamental driver, and all other things can be fixed.
Plus, it may also fix the game console market, which is currently dominated by evildoers who lock down their consoles and consistently act against consumers, by having better games for upstart Android consoles, and possibly a Valve Steam console.
Of course, it's still proprietary software, but I don't think games with high production values can be sustainable as open source until the invention of strong AI that can generate them automatically for free, since it's fundamentally boring to create all the content and even polish game mechanics.