Accounts are already mostly portable (you can easily export all your settings and import into your new account), you just don’t retain posting history.
To retain that… I guess there could be a separate fediverse service that does nothing but allow registering accounts that let you prove that other fediverse accounts all belong to the same person, and then a PR can be made to e.g. Lemmy to honor these links when showing posting history. It’d be quite a messy system.
SpikesOtherDog@ani.social 20 hours ago
There could be a user-centric back end that you could tie in to an account, if it matters. You would export your history to the backend and then log in to the data from the new frontend. That prevents a denial of service caused by numerous large data collections attempting to forward their data all at once.
That then causes me to wonder if data could be hosted separate from the services. That would mean that there would have to be individuals willing to provide that storage and bandwidth.