Strangely, data portability is very low priority.
There really should be some server support for this – but OTOH it’s not paramount. Theoretically, anyone could write a client app that harvests all of a user’s posts and comments into a local DB, and then recreate threads (not comments) in a corresponding community. It would have to add some metadata about the date of the original post. Not great, but could be done.
For cases where the instance is someone else’s. Instances vanish out of the pure blue sometimes. I’ve lost lots of content that way. Also useful for offline reference for those of us who do not have Internet at home.
Interesting, thank you