Uhm, no, I don't see it as being huge per se...do they think the main reason why people are gaming on consoles is extra price they have to pay for WinOS, and that all of a sudden people will jump to PCs just because same builds are now cheaper cause of SteamOS?
Unless they announce their own hardware that can compete in performance with next-gen for same or less money (and big publishers embrace SteamOS), I really doubt Joe Sixpack will be willing to bother with what in essence is yet another take on PC gaming.