MQ is sort of a different beast, actually, because it sits on top of the repository and manages applied patches. From the repository's perspective, it's completely separate from the commit history. IIRC, it started life as sort of an ugly hack and was later folded into the standard distribution when it became popular (well, to the extent that Mercurial is popular). Kind of like how QuickTime started out as a little video platform and eventually got baked into the core Mac OS.

I think what Mark is trying to say here is that he wants us to move toward a workflow where instead of having to generate a patch and upload it to Bugzilla (which MQ is very helpful with), he wants us to be able to commit changes on our own branches and request to have them pulled into the main trunk, no patches needed. There are advantages to be gained from that approach but also tradeoffs to be made.