This spec been there for very long time, and has been adopted by FirefoxOS (deprecated platform). Which exposes low-level access to establish pure TCP and UDP connections with permissions flow by environment.

It exposes many security concerns, that's why WebSockets were more favourable over TCPSocket. We want similar for UDP.

Not having raw TCP means you can't speak to any existing TCP protocol through a browser. It might not be a useful feature but I think that not taking it into account is an issue because most use cases can't be implemented with WebSockets.

Ability to connect to raw TCP or UDP from a browser is a major security hole.

Due to that, WebSockets were created were handshake is handled by browser transparently from developer ensuring port scanning is not possible. As well as to preserver origin-based security model of HTTP. Which we want for WebUDP as well.