I really hope that password managers are a step in this direction. Once they become ubiquitous then everyone effectively already has a "master password" for all

I really hope that password managers are a step in this direction. Once they become ubiquitous then everyone effectively already has a "master password" for all their online identities. It wouldn't even really need to be a 3rd party service. The password managers could hold the keys locally and websites could just use WebAuthn for authentication.