If those rewriting rules have to be server-side, and I think that's what you mean, the answer to that is that browsers don't get to dictate terms to servers that way; browsers can say what they will and won't accept, especially in terms of content type, but URI format isn't generally something the browser can specify.
Comments
What benefit does that have over a unique path/param?
because the browser will always send the unique username to anything at that domain and path
But you could just as easily do:
With just a few rewriting rules.If those rewriting rules have to be server-side, and I think that's what you mean, the answer to that is that browsers don't get to dictate terms to servers that way; browsers can say what they will and won't accept, especially in terms of content type, but URI format isn't generally something the browser can specify.