While it sounds like a good idea in theory, I don't think you realize how much of the scripting language is tied directly to the interface, including /echo, /msg, and just about every event.
This has actually been suggested before but worded in different ways: things like "make mIRC compile scripts to exe" or "allow me to use the script language without mirc.exe" come to mind. Both of these are unrealistic, because mIRC's scripting language and the client are one and the same. The language would have to be completely rewritten to be fully decoupled from the UI. I personally think there are more important things on Khaled's plate right now.
If you want to write a bot that needs no UI you should consider using a better language for the task, like Tcl or Python/Ruby. mIRC's scripting language is built to enhance the client, not the other way around.