Contact cards are great:
But as you can see the entire "NIP" is actually just an event schema definition. It doesn't say what relays to use or give any implementation examples or UX suggestions.
Another argument for doing this:
View Article โ
GitHub
Contact Cards by vitorpamplona ยท Pull Request #761 ยท nostr-protocol/nips
Uses unbound lists to create events that define the relationship between two pubkeys in a public or private manner.
Read here