Both GitHub and BitBucket wikis are already managed by the respective SCMs.

    git clone https://github.com/snowplow/snowplow.wiki.git
    hg clone ssh://hg@bitbucket.org/BruceEckel/python-3-patterns-idioms/wiki

Also, a project atop git does issues: https://github.com/jeffWelling/ticgit

The idea is interesting to me.