Yeah idk. This was a criticism that I brought up of the fundamentals in lemmys structure early on: it selects for, effectively, clones of “whole reddits”, when it should be set up to support more balkanized instances.
Basically, lemmy.ml’s c/Politics is functionally redundant to .worlds c/politics; but thats by design.
What I think would be better would be adding tagging and taking federation a step further. Every post needs a ‘tag’; we steal that part from mastadon. It can have many, but it needs at least one, say #politics in this example.
Then, on instances, federation happens both at the instance level but also at the community level; communities can federate with other communtiies. But all posts get #tagged on the way in the door. Communtiies can then federate or defederate at will, and if neccessary, a community can “branch”; for example, maybe they want to split off US politics from politics; then you grab all the posts with the #US.
As far as an abuse vector. Thats just hang wringing. IF your mods are that abusive for a large sub, you’ve got way bigger issues. Which, if it did ever happen, is something that “forking” would solve. Mod on a power trip? No problem. Fork the community.