If we start up a new tool, it seems like it would be a good opportunity to decide a license of the content submitted by its users.
Submitted code (including actual code and commit messages) would just be under their repository's license(s).
However, the license could apply to other content (e.g. tasks, questions and answers (Ponder), mocks, etc.) unless otherwise specified.
I don't think there's a current license for Bugzilla, so the new license would have to clarify that it does not cover imported Bugzilla content.
I think CC-BY-SA 3.0 is a good candidate. That would allow e.g. importing content from the question and answer module (Ponder) or tasks (Maniphest) to MediaWiki.org (and vice-versa).