I believe more and more people will escape to lemmy sooner or later, and I already see 3 different communities for the same thing (selfhosted) here on lemmy. Time will tell which one will be the most active, but lets assume all of them will be equally active and the desire emerges to combine the two communities about the same thing, is that something possible or intended to be possible with federated services?
What would be nice is to have a system of tags or keywords that can be defined for a community. It would be trivial then to build a sort of multireddit where multiple communities can be aggregated by the tags they belong to.