Hm, some merit to the idea. Browsing the listings of a few sites it seems that Itch.io has more linux games available than any other platform:
itch.io: 3796
SteamOS: 3530
GOG.com: 1350
Desura: 755
Still, even though its not straight forward to include non-steam games into SteamOS it can still run them, and its getting some very active driver/tech support. At this point it might be a better idea to make the Itch.io App compatible with SteamOS to more easily load itch.io/non-steam linux games than to build an entirely new OS, Steam might love the idea of giving SteamOS users access to additional content (or not), and potentially this would give itch.io developers a backdoor into Steam land.