On one hand, even if Valve did start developing for Linux, I'd wager that 99% of their engineers and their tools, as well as all the hardware they develop for (

On one hand, even if Valve did start developing for Linux, I'd wager that 99% of their engineers and their tools, as well as all the hardware they develop for (DirectX is mighty handy), are all based around Windows. You can't just switch that out overnight. I would say without those resources being available it would drasticaly reduce what they could develop. On the other hand, look at what Google/Facebook/GitHub/Android/etc. have done for the open source scene. I keep hearing rumours of Valve making a console, maybe a console/pc hybrid that can run steam on top of linux using their own SDK, I could believe it. It's tricky though, only because so much of Valves infastructure revolves around developing for windows, switching to Linux would cause a lot of their top egineers to be forced out. But christ, if MS forces Valve to leave the PC world and we are stuck with Origin and Games for Windows Live, the PC is officaly dead.