Steam is probably the best shot in a decade at selling consumer software for use on Linux. It'll be interesting to see if it takes off.
The purpose of SteamOS is to power the eventual Steam pseudo-console, and to sit Steam at the centre of game distribution, rather than Microsoft - or rather, put Steam on par with Sony and Microsoft, instead of being a mere middle man.
SteamOS, for all that matters, might as well be a proprietary platform on top of Linux, much like Android is. Its users won't even know it is running linux, nor will they have root access by default - they'll be given an interface which is the primary portal to games (and "Apps") distributed by Steam
Anything "useful" for the rest of linux that comes out of Steam is only likely to be kernel additions, drivers, and other low level stuff that is merely incidental - required by the GPL of Steam, but nothing is going to solve the "problem" of cross-distro packaging, for instance - Steam will only distribute for SteamOS - it makes zero economic sense for them to do anything otherwise.