You're conflating the limitations of Mastodon with the limitations of ActivityPub. ActivityPub does not require "email addresses" for identity - that's a Masto

You're conflating the limitations of Mastodon with the limitations of ActivityPub. ActivityPub does not require "email addresses" for identity - that's a Mastodon idiosyncrasy. Identities in ActivityPub are URLs, so as long as you own your domain you can preserve your identity. That's not too different than your identity being a public key, with the benefit of human readability. Mastodon doesn't offer you export/import of your activities because - again due to its idiosyncrasies - it does not care about past activities. What a user "sees" when they visit another account is only what that account has posted and has already been disseminated to the current account's Mastodon server. A sane approach to past activities would be to load them in response to the user interaction, instead of serving stale data from the db. For this case exporting activities from one service to another would allow for continuity. This could probably be achieved even at protocol level, ActivityPub in its simplest form has enough vocabulary to allow loading a collection and adding its elements to a another one. Some of these things exist in one form or another in other clients than Mastodon.