I don't think they would do that unless Lemmy continues to grow to a point where it challenges Reddit. Then it becomes a technical issue. I don't think they can do that. It was one thing for threads to do it, being designed with that in mind from day 1, but it's completely different for Reddit to do it. There are so many features that just wouldn't make the jump, and so much content that would need to be reworked.
If they were going to do it, it would most likely be a clean break where you just can't access old Reddit content on Lemmy, but all their new stuff would be accessible.
I also just don't see them giving away their content like that after cracking down on the API how they did.
Was trying to get a friend to switch to jellyfin the other day and it turns out he's got a weird Hisense projector that uses VIDAA OS, which does not have a jellyfin app, but DOES have a Plex app. I imagine setups like this are probably limiting Jellyfin's adoption. VIDAA is actually less niche than I thought as well, heaps of cheap-ish TVs and projectors are running it.