It just makes me roll my eyes, they act like it's all so hard to join or leave, when really it isn't. When tumblr had it's nsfw ban, I joined reddit. Now that Tumblr is recovering, I rejoin with a new account. When reddit is having it's api exodus, I join lemmy. All you need is an email and a username, the rest is up to you.
The only real concerns that are in the list are:
The wiki (which could just be a simple copy-paste), though I wouldn't like Lemmy communities to be exact copies of the subreddits. There's many gripes I have with certain subs that should be avoided with Lemmy. As for data, if there's information you think is important to keep, share it. Find communities to share that info with, create ones if there isn't one for the certain thing you want to share. Don't just keep it hanging on reddit. As tvtropes says, keep circulating the tapes.
Splitting the community could be an issue, but a lot of subreddits simply AREN'T community based anymore. I can honestly only think of maybe three off hand that still feel like a community. One of which is only so due to it's somewhat more active discord server.