> or allow Signal to keep a serverside database of contacts ready at all times for users who log in. This is what other messaging services do, and the result is that the servers have a plaintext log of who talks to who on their service, which is the most valuable information a secure messaging service can make available

Why couldn't they just keep using the current system, alongside usernames, for phone number contact discovery? Of course for those who opt into it; imo that's what it should be.