I've seen it talked about a few times across different platforms (Hackernews) where people have pondered the idea of cloning old posts, keeping the poster name but to a non-existent account. Acting as both a way to populate a community and archive content away from Reddit's control.
I haven't seen any examples of this done yet, not sure if anyone has.
It would be a bit of a project, but the most time-consuming part is already done. /r/datahoarder has a backup of reddit comment/post history that goes from the beginning of reddit up to March of 2023 (text only, no media). It's compressed down to about 2TB in size, but already in json format and anyone can download it, would just need some work to convert that to a format a fediverse instance could work with and somehow inject it into a new instance.
It's JSON so it's only text, and it's compressed, but that's still 1 trillion characters assuming it's UTF-16. I've not actually taken a look myself at the data though, I just contributed to let my PC contribute to the project.