Steam (via Proton) generally works, though, for those who wish to use it. (Steam+Proton also works with things downloaded from outside of Steam, too, and has for years[0].)
Proton itself is open-source[1].
If someone wanted to package up standalone Proton binaries for a Linux distro, then I don't see any particular barriers that would prevent that.
On GoG's part, they do provide the ability to just download a game with a web browser (the old-fashioned, DRM-free way). From there, I can manage the games I that own in any way that I choose.
Thus, I'm simply not seeing a problem here that needs solved. I already have the freedom to do whatever I want.
Which part of this situation is broken, do you suppose, and why does GoG in particular need to fix it?
[0]: https://boilingsteam.com/valve-breaks-the-shackles-of-proton...