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.
this was suggested quite a few times already, both here and in Github issues.
question is, how do we get interested people to start implementing it
Developers said in the latest news post that they are aware of community wanting this, but they are way too busy working on some core Lemmy issues, so someone else will have to step up in order to get this to be implemented sooner