Email wanted to be like that and then we got Gmail.
Discussion
User created white lists (what we call "People I follow" or "My Feed" or whatever you call the not global part of your nostr feed) is not feasible with email because part of its purpose was to allow messages from people you've never met before.
Your timeline has notes from people you don't follow, mostly in the replies to people that you follow.
This is important for you to discover new content and new people.
Every system has to have a way to discover new content and that is its Achilles heel.
Show me how you have learned from the mistakes of the past 40 years. Nostr hasn't.