Thanks for your feedback!
You can already export followers to a .csv file thanks to the link appearing at the bottom of your list of subscribers.
However, we do not allow you to edit or import subscribers to that list; as much as we want to allow you to import subscribers from third-party services, we also want Jetpack Subscriptions to remain as efficient as possible.
If spammers were to start importing massive lists of subscribers into Jetpack, email providers might start sending all Jetpack emails to spam, including the ones coming from non-spammers.
It doesn't mean we're not considering this option though; we will just need to make sure Jetpack is not used by spammers first! :)