This would allow server environments (specifically talking about nodejs/undici) that implement WebSocket some flexibility, for example, to add custom headers, etc. While we could change it on our side, it would be incompatible with other implementations. Similarly, it'll cause type issues with people who use typescript in cross-env packages (ie. nodejs/undici#1943).

Proposed change:

dictionary WebSocketInit {
  protocols: DOMString or sequence<DOMString>
}

interface WebSocket : EventTarget {
  constructor(USVString url, optional (DOMString or sequence<DOMString> or WebSocketInit) options = []);