As far as I know this isn’t a feature that exists, but I know the protocol should make it fairly easy.
What I’m thinking is for Lemmy to basically have the option to inherit the comment thread when posting a URL to another fediverse service.
E.g. If crossposting a Lemmy thread, you get a tickbox saying “inherit comment section” or something and it makes the new thread effectively a symlink to the original.
This could also be used to bootstrap other fediverse services like pixelfed and peertube by enabling people to comment directly from their Lemmy instance.
I think the necessity for moderators to curate the experience for the members of the community is overrated.
I’ve seen very selected cases where that kind of thing is done to good effect. /r/AskHistorians is the most obvious example. I’ve seen a whole lot of cases where there are moderators who are abusing their ability to control the conversation, going well beyond just keeping everything on the rails, and deciding for themselves what people in the comments are and aren’t allowed to say.
Personally, I think merging the comments threads from multiple communities would be a clear benefit, in part specifically because it would eliminate that ability for moderators to decide how they want to shape the comments to look like.
To deal with moderation conflicts you could basically just unlink the thread.
Also we could also just add flags to activitypub messages on creating posts to tell the boosting server whether or not merging is permitted.
If you’ve worked hard on something and want everyone to see it, set it to True and people can boost it to different communities.
If it’s something personal or an in-joke that you only want to be advertised to the community it’s posted in set it to False and the option won’t be available when cross posting in the UI.