My suggestion on GitHub was to let instance admin create a local /g/ grouping, with the freedom in how they utilise a /g/ group.
Some people argued that they should be able to make it per account, like a multireddit, but the point was for new and general users having easier access to broader fediverse content.
The instance admin would only need to do some legwork at first, then they could add to it as they go along. The barrier of entry for new users finding which communities outside of their instance is substantial.
If there are 5 different instances with the same community, to subscribe to all of them you have to go find them all.
If kbin had a feature to combine them in groups like this, when you went to subscribe to one version of the community, it could let you subscribe to all of them at once. Without having to hunt them down.