Do people use that publish-subsribe model within a process rather than between processes? Any time I've encountered the 'event bus' model it's been for 'enterprise' (for lack of a better term) scale integration (i.e. gluing together applications across an organisation).

Sure, no matter what kind of programs. To get an idea, take a look at the example code at the end of the page: https://github.com/spinettaro/delphi-event-bus