Depends on how one thinks of "mass," since (a) there is an unholy amount of tooling out there which only speaks the GitHub API (not even mentioning GitLab, Gitea, ...) and (b) AIUI the Fossil folks abhor history mutation which is great for them and really not great for a subset of git users. I get the lightweight impression that they took Mercurial's "please don't" and turned it up to 11