Right. The server knows a user by their identity key, not necessarily by the device that the key is on. Since keys are lightweight, synchronizing them across devices is akin to managing metadata.

Further, servers are free to keep private information on identities, with the understanding that identities are so flimsy that any single identity profile is not worth data-mining. This won't prevent tracking from truly big players, like Google, AWS, or Cloudflare, but it greatly cuts down on their ability.

This reminds me of moot's concept of prismatic identity.