Updated SteamOS partner guidelines seem to point to an imminent full-scale launch of SteamOS on other gaming handhelds out of the box, nevermind simply as an ISO for gamers to install on their own machines. Previous work suggests the Asus ROG Ally may be among the first to receive "Powered by SteamOS" certification.
I use my Deck docked regularly. In desktop use I see no benefit over Fedora and alike.