I would certainly /not/ use a separate "beta-test" wiki if it isn't Wikipedia, because that's extra work and it's boring compared to Wikipedia. I'm sure at least 90% of the users feel that way.
Fair point, and I think you're right in that test wikis maybe aren't used as much as they could be, mostly because their limited content means they're just not very interesting to use.
I really like that idea. I would use such a beta instance and report problems as I find them (which is the purpose of a beta-test).
But from what Tim was saying, I think (and someone please correct me if I'm wrong here) that the idea was to have a test wiki which would be updated as one of the last steps before rolling a software update out onto the cluster. The beta site would be updated, and then there would be a quick smoke test by the person doing the roll out ("does the front page look normal?", "do a few other pages look normal?"), and if nothing abnormal was observed, then it would be rolled out onto the cluster.
As a consequence of this, from a tester's point of view, you'd normally only have a window of a few minutes in which the software you were testing differed from the software elsewhere.
Basically this setup would be useful as a quality-control checklist item to the person doing the rollout; however it would not be useful for beta-testers, because you're not actually beta-testing anything new (apart from in the brief few minutes before rollout).
So if you want to use the bleeding edge, report issues found, and act as an early-adopter who gives early-warning feedback on changes before they reach the general population, then I think this may not be what you're looking for.
Of course, I could have misunderstood what was being proposed.
All the best, Nick.