To me this is basically a necessary feature of a fediverse app that wants to be similar to Reddit.
Smaller communities are fantastic, but one of the unique appeals of Reddit was that for the largest communities, they were likely one of the most populated communities for each topic available. So posting to that community ensured the broadest reach, and greatest likelihood of engagement or getting one's questions answered.
I hope we can find a federated way of providing a similar experience. Perhaps via replication between instances.