I've been thinking that it is probably easier to move a community from a platform like Reddit to the Fediverse than it is from Twitter. I have used both Twitter and Reddit a lot, but have moved off Twitter and now use Mastodon. Mastodon works pretty well for me, but it's taken a lot of work to get there, and there are parts of the communities (mostly related to my work) I want to connect with that just don't exist on Mastodon.
But the big difference between Reddit/Lemmy and Twitter/Mastodon is that on Reddit/Lemmy I am interested in communities for topics that are mostly hobbies/entertainment etc. for me, so I don't really care about who I'm interacting with... I can't really name more than a handful of regular users or mods on the Reddit subs I've been using for more than a decade. But it's not really important for interacting there, because it's about interacting with people who have an interest in a particular topic no matter who they are. On Twitter/Mastodon (at least how I use it), the specific people I'm interacting with are more important.
So it seems the "lock in" of Reddit is weaker than Twitter, and I think it'll be quicker to establish communities here. A community on Lemmy with a few hundred people contributing (posts/comments) is already pretty successful and enjoyable. It doesn't matter that the equivalent community on Reddit has over a million people (and in fact it's often better if it's smaller!).
That weaker lock in and the fact that Reddit seems to be massively undervaluing the contribution mods and third-party app devs make to the platform make me think Reddit is going to quickly regret this whole fiasco.