Valve has confirmed that it is working on bringing SteamOS support to rival handheld devices like the ROG Ally. Dual booting into Windows on the Steam Deck is still far away, though.
Bazzite is basically exactly this already. If you have an AMD gpu you can boot straight into steam. The desktop mode uses KDE like the Steam Deck and the package manager makes it much easier to layer in additional system packages which is kind of a pain on the Deck. Plus there are some additional gaming specific tweaks popularized by tools like cryoutility included by default.
Bazzite is basically exactly this already. If you have an AMD gpu you can boot straight into steam. The desktop mode uses KDE like the Steam Deck and the package manager makes it much easier to layer in additional system packages which is kind of a pain on the Deck. Plus there are some additional gaming specific tweaks popularized by tools like cryoutility included by default.