> Enforce scope (namespace) requirement, and require external verification (reverse DNS for example).
Who the heck says everyone who publishes a library has a domain? That seems absurd.
Why don't you? It costs around $20 per year. Every serious computer nerd should have one, and a web server with at least a basic homepage.
Sonatype allows "io.github.<username>" as a valid groupId and has a process to verify ownership. I am sure other providers like GitLab can work on this.