Any reviewer should be able to mark an extension as "needing admin review" (or "questionable", perhaps), to help get attention for hard cases or possible abuse. They could use this during review to call out cases that are in blurry policy areas, or after approval to draw attention to an extension that may have a serious issue.

This could just involve a reviewer whiteboard for extensions in the queue. That would also help with more than one person reviewing stuff/testing on mutliple platforms etc.

That only addresses the pre-approval case, though, and doesn't let us build an admin-review queue or send mail or otherwise actively draw attention to these cases. Keeping a history of reviewer comments on a given extension is better done in the context of something like bug 335373, IMO.

*** Bug 294292 has been marked as a duplicate of this bug. ***

I think the admin mailing list would suffice for something like this.

I don't. The mailing list provides a crappy audit trail.

From the "Review add-on" page, you can now "Request Super-Review" which notifies admins to look at the add-on.