This makes me wonder if there could ever be a way to allow some requests to be on one group and other requests for the same wiki could be another group.

e.g. users could opt-in to being a canary or some users could be randomly selected.

When would this not work? If a newer version required schema change then have to stop using old version after applying new schema? but that isn't very common? any other complications?

-Jeremyb