I'm not so sure that the 'p' tags in follow lists were meant to notify those people, like 'p' tags in most events do. They were the only tag to carry a pubkey.

In Mosaic I explicitly indicate a "Notify Public Key" tag, and follow lists (not yet defined there) will use a different pubkey tag that doesn't carry the "notify" meaning.

This is because I don't think it is necessary or even very useful to tell someone you are following them, and it erodes privacy. It's tracking. It's like going to a web page and giving them a cookie.