There you go, we could easily do it the same way, like:
Bitcoin can answer port 8330 on local loopback just as it does for JSON-RPC on 8332. It would give an HTTP answer.
I think we can do that.
Although it would be possible for Bitcoin to take care of business in the HTTP response by presenting HTML UI to the user, as a user I would wonder if some website is trying to trick me or if I'm really talking to my own Bitcoin server.
127.0.0.1 loopback is accessible by any user on the machine, it doesn't have per-user separation, but it's OK because it would only serve the convenience function of pre-filling the fields in a dialog. You'd still have to press Send. We'd have to make sure the Send button is not selected so it couldn't jump into the foreground while you're typing a space or enter.