> The design goals of the Internet you're referring to are about networks not going offline, a global routing table with individual entries for every user is not sustainable.

With a bit of a redesign it would be. Most mesh networks tackle this problem. In the worst case, a routing table entry for every human in the world is only 8 billion entries, which would fit in RAM on a typical server today. And every optimization you do dramatically reduces that number (eg. make users who have similar network configs and peers have neighbouring addresses, allowing you to coalesce potentially millions of users into a single route)