It’s a solution, but I don’t like it.

1.- It’s less resilient. If (more like when) one server goes down it could take the only community in a topic with it.

2.- If the moderators for the community of your interest are kind of dickwads, or absent, or malicious, you have no alternative.

3.- Federation can create weird problems. If your account instance is not the community’s one, you could be effectively banned, without doing anything wrong.

4.- Creates a perverse incentive for using the biggest instance you can for both creating communities and users. Some of the bigger Lemmy instances already are under heavy load and having problems to stay online. Imagine if we discourage using small instances.

Some mechanisms to “merge” communities across servers would be cool addition. Every Android community in every server that still federates with each other lists every post in all of them. Moderators moderate the posts in their instance. Link repetition is the same as inside of one single community. If one of the composing communities moderator team doesn’t does it’s part it could be expelled from the composite. Like a soft de-federation.

Just rambling. It’s a complex problem.