No “if”, no “would”, we are millions of gamers using our (portable) PC with SteamOS running on it for few years now already.
As others have pointed out already, the SteamDeck is exactly that. I even travel with it, use desktop mode with my BT mouse&keyboard with a USB-to-HDMI adapter and work on large screen and do my presentations with video projectors.
If they were to sell a desktop too… well I have a Corsair ONE already, naming a gaming desktop (2080Ti) with a very small footprint and relatively silent. It is not easily upgradable due to how compact it is (but can be done) so if I were to have an equivalent of it from Steam and they were to keep on contributing to FLOSS it would probably be an even easier buy because I trust their RMA and I imagine I wouldn’t pay a “Windows tax” with it as it would “only” come with SteamOS.
TL;DR: I’d prepare my credit card.
