It's always difficult to test non-local effects in open betas; since the world view doesn't distinguish between beta and live instances, in practice you have to coordinate offline instead of just dropping in and looking for another tester online.

While changing the instance search system just for open beta builds is probably a big project, a simple thing you can do today to help improve this is to simply put a suggested beta instance launch link in the announcement post. While anyone can make such a link, ones posted in the discussion channel tend to scroll off quickly and are less effective as a result. This would provide a quick way to meet up with other testers with a minimum of coordination.