Right now that data is not truly equivalent. E.g. twitter/fb have email addresses, and use them to notify friends, but they won't give you your followers' email

Right now that data is not truly equivalent. E.g. twitter/fb have email addresses, and use them to notify friends, but they won't give you your followers' email list. There could be a way to ask your followers to give them for example, or at least a hash of it, so they can be discovered in another network. The issue here is that whatever value is in friend lists /subscribers is locked into these companies, but in reality it's the users who have earned it.