[dyingkneepad]

Will you also mirror CI infrastructure, issues, pages, documentation, API-consulting scripts, etc?

Also, pushing to a mirror is not exactly the thing you want.

What makes apt easier is that pretty much everybody is just downloading from the source or from a mirror. When the source stops, mirrors don't get updated and everything still works. That's very different from the usage model that people have with Github.

Gihub/Gitlab have extended the Git usage model very much, they are not just git. You can't easily migrate away from them to another git offering (and not even very easily between both).