Correct me if I'm wrong, but the denizens of Tumblr largely fled to Twitter, right? Given that the Twitter is now in the hands of Elon Musk, where would Redditfugees even flee to? Fediverse?
For schizoposting purposes, bluesky is my best guess.
The issue with the fediverse is that it mostly only attracts niche people, just like the endless amount of reddit clones over the years have only ever thrived for an extremely limited population (ovarit->women, rdrama for, uh, marsey enthousiasts), or extreme thinking (remember voat?).
99% of Lemmy instances are exactly that shit, and barely anybody use them anymore.
EDIT: To further support my point, of the top 10 public lemmy instances, exactly ONE is general purpose english, 4 are for tech, two are region specific, one is for porn, one is for trannies, and one is for commies.
That's 17970 monthly active (posting) users between all of them. Reddit claims approx 100 million daily active (reading) users.
Even if only 0.1% of users interact with reddit, that's still over 5.5x more interactions
per day on reddit, than per month on the top 10 lemmy instances.
Discord isn't a viable option because it's live chat to a narrow group of people, it harms the narcissist when the karma doesn't go up. At best it's a side bitch and not the main course.
Maybe a tumblr remigration might be possible, or even a wildcard service nobody knows about, we need to hold redditor safaris to find out.