The copyright applies to the source code the copyright is written on. Lawyers then argue who owns the "project" (GitHub organization/repository). For example, the copyright is not applied to the issues in the issue tracker.

But the argument is about whether the .NET Foundation could do such a thing. The argument is whether they should. And, the .NET Foundation chooses that they should take over the projects, project maintainers can make different decisions themselves.

None of this has been decided yet.