It seems to me (as a casual observer, having read the related threads about module names and such) that there are contradictory goals here. From the document linked in the original post, about the goals of the SSWG:
It seems to me that not all packages that might be of interest to developers of server applications belong under the SSWG umbrella. There are hurdles to pass to try and ensure quality, integration with other SSWG packages like NIO & logging, and distinguish experimental libraries from stable, production-ready ones that are being actively maintained. It is by definition something of an exclusive list that prioritises quality over quantity.
Even if library authors need to develop their packages elsewhere, I still think it would be worth having an official, SSWG-controlled mirror at least.
It's important to give credit where its due, but I'm not sure it necessarily needs to be in the form of the repository's URL and ownership. Would some kind of prominent attribution in the README be sufficient?
It's also quite common to see projects which are maintained by somebody other than the original project author. In such cases URL-based attribution gets the wrong person's name out. For open-source projects where longevity is key, a stable, neutral URL is best for everybody IMO. Even if it is only a mirror of some other, author-controlled repository.