There was some work to address this issue with federation in Gitea, but I haven't kept up with how well that went. Our practical solution was to just mirror our Gitea repos into GitHub. That way they're discoverable, releases can be downloaded, and so on. Not a perfect solution because users get confused as to why they can't open issues, etc.

I was one of the members who was a part of the initial grant for federation in Gitea, but sadly due to illness and other similar neither I nor my teammate were able to work on the grant (so no funding ended up being released), however the work we did start was completed, and we have continued to work on foundations since. Since spam/moderation/limitations are so significant we are focused on that portion first, since we don't want to open up another vector for it without having at least the minimum of protections in place. We have also been extremely fortunate to have experienced developers who do work on existing federated software share so much of their time, expertise, and experiences with us to help shape our work.

That would be good for following, but I'd worry about contributions. Single-sign-on would help but if you're going to ask the user to create a new username+password to log a bug you're not going to get bugs from anybody except your most hardcore users.

Also, unified dashboards/notifications are so useful (even though Github's notification UI is a bit mediocre, imho).