I don't really think anybody expects that to happen. As long as a large enough number of people move, it can succeed.

But people don’t care. Homelab subreddit created a forum and after 5 days, the number of registered users on that forum is 18. Selfhosted subreddit did the same thing and activity on their forum is similarly low. If people on “selfhosted” subreddit don’t want to move to a selfhosted alternative, I don’t know if there is any hope for other communities.

The selfhosted community on Lemmy (https://lemmy.world/c/selfhosted) is up to 12.5k subscribers and seems fairly active so it's possible there might be enough people who care this time for it to work.

These things tend to not work until all of a sudden they do.

I think the communities would benefit from becoming smaller. I avoided any large subreddits because the noise ratio was awful. The smaller ones were much better.

The trick is to both (1) promote equivalent communitie to existing Reddits - let them know there are alternaives to being a serf -- and (2) start posting on there. Be the change you want to see!

The federated future for social is coming, albeit slowly in fits and starts. What is nice is that many of the communities on these two are shared because it is the fediverse.

EDIT: Downvoted why?

What about migrating historic data from Reddit ? Is that possible?

From a technical standpoint: Archive.org is archiving Reddit data. So someone just needs to write an importer for that data. I would have suggested reading from Reddit's APIs directly but they are shutting those down.

From a legal standpoint: I am unsure.

Do they archive nsfw too?

Edit: I checked, and Archive.org seems to be snapshotting once per quarter or less. Not a realistic strategy for any sub with even modest traffic.

Or legal?

I'm certain you got downvoted over the word 'serf'. I upvoted because my reaction to that framing is more positive, but it's not a framing I would use, myself, because I would expect to get some flak for it.