I don't know in depth how Proton works internally, but I think it includes non free DLLs, including DRM support, to improve compatibility with Windows games. If my understanding is correct, shipping Proton and games that depend on it as part of Guix would be a tacit endorsement of proprietary software that exercises unjust control over users. The GNU project, as a matter of policy, does not recommend non free software components, or free components like DRM that are exclusively useful for restraining user freedoms, so that may be a dead end.

I like your energy in this thread though and agree that it would be great if we could help gamers break out of the ugly Steam ecosystem. Itch is an independent game distributor and they also publish all their client code as free software: https://github.com/itchio

Bringing Itch to Guix might be an interesting project, if we could find a way to modify the client so that it does not recommend any games that are not free software. There's a healthy and growing list of such games here: https://itch.io/games/tag-open-source

We might have to build our own game discovery portal to replace the upstream itch.io storefront, but that would be a really nice thing to have in general.

Itch has its own tools for game developers to build their game and ship updates to their users. For example, they designed their own protocol for shipping new game builds using minimal resources: https://github.com/itchio/wharf

It would be beneficial if Guix could learn some of Itch's tricks, to support fast moving projects that want to ship frequent updates to users.