Valve seems to be testing ARM64 and Android support on Steam, as per a new SteamDB leak. Popular titles like Left 4 Dead 2 and Garry's Mod are being tested with "proton-arm64" tags, among others. This could hint towards new future Valve hardware running on ARM64 architecture.
Valve will do with SteamOS what’s good for them and their profits. They aren’t in this for idealism.