People have discussed the portability problem for ages--"walled garden" as a tech concept goes at least as far back as AOL--but all the solutions so far depend on the good graces of the very thing that's likely to create the situation where you need it. I can't run a Google Takeout if a stray cosmic ray causes a chain of events that destroys my account, for example.
I want more companies to start taking the approach Bluesky has where the data is designed to outlive the system.