Unless GitHub reverts this change, it is now impossible for researchers to view the discussion from issues and pull requests in the xz repository.
I cannot think of a legitimate reason for GitHub to censor this content: the two members of the organization had already had their accounts suspended by GitHub; it's not as if they could forcibly push over the content in the repo.
I'm not sure what to make of this move by GitHub/Microsoft, but it sure isn't a good look.