Anything that works client side or via a 3rd party aggregator is going to be a hassle for moderation.
I guess a subscription option that moderators can opt in themselves would be OK, but I don't think it will be used much.
In the end it is simply a wrong impression that these communities are duplicates. A community is part of a specific server and usually has a set of regular contributors. This together is the community and not some rather arbitrary name that it might also share with other communities.