A very easy solution would be for Steam to transition to the GOG approach optionally: Preserve games without any sort of DRM or online-only feature. Releases past a set amount of time could drop DRM (they already have this option AFAIK) and they would also need to have a sort of non-steam-services connected variant.

Combine this with completely FOSS SteamOS/Steam Client, and Valve would do everything right.