Is there a Gollum-like Wiki (Gollum uses a Git repo to store its pages) based on Mercurial (instead of Git)?
Please take a look at Hatta. That is a Mercurial-driven wiki where you can edit the pages online and thus create new revisions in the underlying repository.
MoinMoin 2.0 will also support hg as storage backend.
It's still some ways off, though:
"Maybe end of 2011" is maybe not totally unrealistic.