gerrithub builds on top of github, so... ick. But you're the one that would be stuck maintaining it, so it's definitely your call.
We use it at work for some things and it seems to mostly just use github for auth, an importable repository directory, etc. You don't have to use pull requests (and indeed we ignore them). Otherwise I think it functions just like a regular gerrit.
I did a little web searching and reading after sending my last message, and I wonder if that is true? hg-git provides the ability to pull from and push to a remote git repository from within mercurial. Wouldn't that be sufficient for interacting with gerrit?
But they're not currently pushing, they're sending patches to the list, and mostly using mq for maintaining those patches on top of their repo (like quilt/guilt). In order to push from mercurial, you'd have to at least commit those patches and then you've got a more complicated problem for revising patches due to feedback, especially if tip is moving underneath.
Regardless, I only think this is doable if all the major players are willing to move to git/gerrit. Lets give them time to respond (from their respective timezones).
--Dan