It's doomsday if Linux starts outperforming Windows. If SteamOS for PC still required me to dual boot - which I already do - but guaranteed is get 100% windows performance or better, then that would be the official end.
It's not clear to me this couldn't happen either: I am very willing to hand over the entire PC configuration if the promise I get in return is "your games will run as fast as it is possible to run them".