Mastodon is a good example and counterexample of this trend. Gab was the biggest Mastodon instance, largely populated by the kinds of people pre-Musk Twitter banned or limited (and their followers.)
But the second (post-Musk) wave wasn't people who got banned, it was people leaving because they didn't like Musk and/or his changes to Twitter. And Reddit's own userbase came from Digg in much the same way.
Imagine if Mastodon had been easy to migrate to, Twitter would have collapsed like a popped balloon.
Reddit has a natural administrative/scalability partition boundary though, which makes federation much easier. I think a federated reddit would work better than Mastodon has.