373 specifically is about the CardDAV format; this feature request is more generic, just wanting the ability to add a person's name and email address without having a GPG key for them (perhaps they're a middleman, who's going to pass along the encrypted message to another party? Or we just want to send them a signed message, not an encrypted one, so they can verify it's from us?). I think that functionality can be done fairly simply, without having to take the additional step of also being a CardDAV client.
It seems like the only way to get contacts into the client is to import someone's gpg key. Is a proper addressbook function on the roasmap?