The main issue with the size of .world so far is just the technical stuff. Lemmy hasn't really been tested at this scale before so we're seeing various bugs and federation issues that have probably never been seen before either.

Personally I don't think the Beehaw thing was a problem for people outside of the walled garden, only for those in it. I had an account there but had to move off to keep access to my fave communities, whereas the ones on there I was using from my .world account all have alternatives elsewhere so that account wasn't "punished" like my Beehaw one was. This is of course a huge advantage of the community split, one instance can't arbitrarily cut off your access to a certain topic.

What I've been doing is just subbing to all communities for a given interest, and seeing how it goes. Sometimes there are different goals /atmosphere in each, or sometimes I'll just cross-post to all of them and see where folks are biting. I've already seen a couple of very niche communities start redirecting people to the bigger competitor so some amount of centralisation is just going to be natural over time.