But then it wouldn't be open-source anymore, would it? Making the willingness of people to contribute likely much smaller. You don't really have the safety of having an easy way to fork either, if all you can fork is a 2-year old version (which plugins are likely not compatible with anymore).

It would also (deservedly) likely anger a large part of the existing community, especially the ones most involved, like plugin authors, who put their time in assuming their contributing to an open-source ecosystem.

Thus, I believe that ship has sailed the moment they made it open-source in the first place.