According to Wikipedia, they already officially support the Lenovo Legion Go S.

Not sure what you mean by "not great," the Steam Deck is awesome. The one in our household is like 3 years old and still sees daily use. They have been very well received by the PC gaming community.

SteamOS is mostly just the regular Steam client on top of Linux. You will get more or less the same overall experience by starting with a reasonably capable GPU, then installing any mainstream Linux distro, then installing the Steam client, and making a few tweaks. Valve has been very active in upstreaming fixes and features to upstream projects like the Linux kernel and Wine, so the Steam Deck (and soon Steam Machine) doesn't actually have any special sauce, it's just a nice self-contained unit for those who just want to play games and not be bothered by the OS under the hood.