They generally run Linux without issue already... that said, pre-installed options would be nice, not sure if SteamOS is the most appropriate. Probably Pop, Cachy or Bazzite, and given that Pop comes from a competitor, unlikely.
We're talking about making it popular though, so shipping with it is the important part. You can also install Windows on the Steam Deck but that doesn't make the Steam Deck a win for Windows.
It's already happening. Lenovo released a SteamOS variant of the The Lenovo Legion Go S.