I guess the ‘simple’ way of doing this would be adding tags to communities like ‘art’ ‘hobbies’ ‘sport’ ‘football’ etc. This might then let the app suggest others based on the tags you are subscribed to.
It would probably still require some AI/analytics to work out the links based on user activity in different communities/tags but I think it would make it easier to group interests and promote smaller communities.
It could also improve Lemmy visibility in Masterdon if the tags are used as hashtags or something. (Would require more work)