SolanQ: The other plugins are very much in a grey area, which is why GOG probably chooses not to host them directly. As long as they're developed and hosted by the community, it's unlikely the associated companies will take any action, but if GOG built them into Galaxy and made them "official" that might very well change.
Barleyman: What are you talking about? Galaxy installs the plugins for you, they're very much official part and parcel of it.
As for adopting this new plugin, GOG could do it exactly the same way they're doing it now. But it might take a little bit of working hours to test it and integrate it into the installer properly, and that's unlikely to happen. Just look at the Ubisoft debacle, fixed by users ages ago but fix is not incorporated into galaxy installation.
Personally, I'd jump back from playnite the second Steam started working again.
GOG has coded a search function and one-click install process into Galaxy for community plugins, yes, but the actual files are downloaded from this Github page here:
https://github.com/FriendsOfGalaxy GOG neither own nor operate that account. In fact right now no one seems to have access to it. It seems to have been abandoned about 2 years ago, which is the reason for all of these issues.
Galaxy completely obscures where it's installing its plugins from, so I was just confused at first as to why GOG can't just... apply these fixes. The only reason I learned about the existence of that Github account is because there are some plugins that aren't on there, and thus not "searchable" within Galaxy, but I came across some mention of their existence on the forum - and from there I fell down the rabbithole of "OMG, all of these integrations are just an open-source Github project that isn't managed by GOG at all?!"
Don't think for a moment that I don't believe this entire situation is stupid. I've simply had a few years to get over my astonishment. XD
Edit: the good news is that GOG has taken notice of the efforts by ABaumher to fix the Steam plugin and reached out to him. So there is some hope that Galaxy may be updated in the future to retrieve these plugins from a different Github repository that is actively maintained (GOG Nebula), so that plugins can automatically receive updates through Galaxy again.