To be fair, the MQ and rebase extensions are shipped with mercurial, just not enabled by default. They share the same bug tracker as the main project and in my experience are just as well documented and tested as other bits of Mercurial.
It's also been my experience that non-expert users don't understand the repository DAG model well enough to perform history rewriting reliably and without error, which I think is one reason these features are disabled by default.
Finally, as of Mercurial 2.1 they now have the concept of "phases" of commits which make local non-shared commits mutable whereas commits which have already been shared are immutable. This new feature is a first step to safer history editing operations becoming more mainstream mercurial commands.
It's also been my experience that non-expert users don't understand the repository DAG model well enough to perform history rewriting reliably and without error, which I think is one reason these features are disabled by default.
Finally, as of Mercurial 2.1 they now have the concept of "phases" of commits which make local non-shared commits mutable whereas commits which have already been shared are immutable. This new feature is a first step to safer history editing operations becoming more mainstream mercurial commands.