Although it's not yet freely accessible to testers, an update to Steam's beta client suggests Valve is already prepping for the in-home streaming it announced alongside SteamOS.
The renowned Steam sleuths at Steam Database uncovered the in-home streaming feature after a new beta client update; it's not immediately accessible, and only advances users should fiddle about to unearth it.
Unfortunately, even if you do unlock it it's not yet functional, but the site managed to harvest some details.
It looks like SteamOS will allow users to hook multiple sources up to a local network for streaming around the house, and browse available sources via Big Picture mode. Administrators will be able to manage both bandwidth and framerate to maximise performance.
It's not yet clear how the system will cope with the fact that at present you can only log into one machine at a time with the same Steam ID; presumably some sort of update will make allowances for this.