Not sure if you guys ever played .hack... the "fictional" "Altima" OS that you use for the game menu was pretty cool looking, and it has a lot of resemblance with the current widely used sony XMB... I don't think it's really hard to modify that XMB to make it a 'functional' OS...
However, I don't think it'll have a stronghold in the PC market where it's more of a trend to have do-it-yourself PC... None the less, the PS3 can EASILY be modified to become a "2nd" media PC in the house that serve as a media hub, light office document etc... And I think Sony is slowly bending toward that route.