Discovering new communities that share names and topics will be the biggest core improvement in my opinion. Like having a way for an instance to poll all federated instances for communities with the same name or with a name that includes a term to easily add would be awesome.
Then the ability to combine them into subsets of your siscriptions by whatever topic you want would be awesome. Like instead of subscriptions as a while you could have 'Tabletop Gaming' with various 40k, CAV, BattleTech, and other games grouped how you want or subgroups for each game.