Here is an unfinished idea, food for thoughts. Since there is no way to not centralize a domain name, let say a software project has no domain name and its home page is a wikipedia page or section in a wikipedia page or a wikidata entry. Although it is very difficult to create a web page for a project, adding a section in an existing page is comparatively easier. It could be a section in forges that explains the concept of federated forges with a table with a list of projects that are independent of any forge and whose sole purpose is to act as a federation proxy between them. And one entry would be about fedeproxy.eu, another about a fork of fedeproxy.eu under the domain example.eu etc.
This wikipedia page is how people know about the project and it is governed by the wikipedia rules, independent of any individual involved in the project. And this wikipedia page will list all the domain names where the project can be found instead of a single domain name. This list will presumably be a table that also explains the differences between each domain name.
To ensure this list is not merely a list of forks and one domain name becomes the de-facto standard, each website would never link itself but link the wikipedia page instead or the wikidata resource. For instance when publishing a blog article, the link to the project would be to the wikipedia page and not to the domain name. The same could be done for releases with wikidata.
The wikipedia page / wikidata entry would be about the project and explain that deliberate strategy to workaround domain name centralization. When a domain name is created and deviates from this strategy, it would no longer be listed in the wikipedia page because it would no longer match the description.
It is more involved than it should be. But maybe the core idea of using wikipedia/wikidata as an indirection to multiple domain names is something interesting.