But then you have an entire front end written in Tcl or some other non-COBOL language (to continue the above example,) right?

Or is there a way to run Tk as a daemon?

Believe you have to do that anyways unless you are going to create full language bindings as tkinter and the like do. I don't know the Tk API in full but I don't believe it provides ways to create widgets, just interact with them more directly. Perhaps someone more knowledgeable will fill in the gaps here, I learned what I needed of the Tk API and called it good.