Protocol is open, anyone can rewrite a federation client that pulls data off proprietary servers as a last resort. This is why federation is great. Besides, you can't close an open source project, you have to create new, closed parts to have them. That's how mariadb and galera took a chunk off mysql user base and how libreoffice became a successor of openoffice.

As a side note, I wish we could move accounts and even communities between instances, based on some kind of two way handshake agreement.