That sounds like a deficiency of browsers, not of URLs. Browsers can already make arbitrary HTTP requests, and there are some rudimentary ways to expose this in

That sounds like a deficiency of browsers, not of URLs. Browsers can already make arbitrary HTTP requests, and there are some rudimentary ways to expose this in hypertext (such as forms or XHR), but there’s nothing stopping a browser from letting you dump a full HTTP request into a text field and sending it.