Mastodon currently does not support importing posts or media due to technical limitations, but your archive can be viewed by any software that understands how to parse Activity Streams 2.0 documents.
Your posts will not be moved, due to technical limitations. There is also a 30 day cooldown period in which you cannot migrate again, so be very careful before using this option!
It’s not that easy to implement. Any feature that lets you import posts would just be a bypass for any kind of spam protection or rate limit. You could just “import” thousands of spam posts at a time, without the server being able to prevent it, because it seems totally legitimate.
Mastodon still doesn’t allow account import
https://docs.joinmastodon.org/user/moving/#export
It’s not that easy to implement. Any feature that lets you import posts would just be a bypass for any kind of spam protection or rate limit. You could just “import” thousands of spam posts at a time, without the server being able to prevent it, because it seems totally legitimate.