One issue with the fediverse right now is that there are many redundant communities. Like !firstname.lastname@example.org, !email@example.com, !firstname.lastname@example.org, etc all having essentially the same topic.
I think the easiest solution to this is to take reddit’s multireddit feature, allowing users to create their own “technology” multi-community that includes all the popular technology communities from all the instances. Thanks to federation, the user could interact with this multi as if it was one big community. Perhaps a way to share the multi with others so that all the component communities get federate-mirrored to the new user’s instance would be needed too.