Asklemmy

I think this is currently one of the biggest problem of Lemmy on the UX department. Non technical users from Reddit will only expect one "subreddit" for a theme, but if they search on Lemmy, they'll find more than one community with the same topic, and it'll confuse them and make them less likely to come back.

But that's the way how Fediverse work, so I don't think combining two communities should be done from the Fediverse side, but rather each Lemmy instance can curate a "playlist" or "multireddit" that has some of the biggest communities from the users' server and other federated servers about the same topic, and users can subscribe to the "playlist" rather than individual community.

This would be cool and useful

I don't know how Lemmy or Kbin work internally, but I believe merging 2 communities could be similar to a user migrating to another server. Account migration on the Fediverse works by having the old account being setup as a pointer to the new account, effectively merging the old one into the new one. Followers of the old account will automatically follow the new account.

Since Lemmy and Kbin's communities are, behind the scene, like user accounts boosting messages posted in them, you can see how a community could be marked as "migrating" into the new one.

Another option would be for a community A to automatically boost/repost all posts from a community B, effectively bringing all messages of B into A.

Note that these are pure speculation on my part. I don't know if any of this is possible 😅

This would be a very useful feature. Hopefully it will be added at some point!