Each user in each course should have a personal forum, probably on their home page.

This forum could have multiple functionality, bringing together discussion from all over Moodle.

Firstly, existing threads started by the user elsewhere in Moodle appear here (as now).

Secondly, student's can start discussions of their own. They could be directed to the teacher (discussion remains private between teacher and student) or to the class in general (like a blog entry, and these public entries for all students could be accessible from a single blog forum).

If journals, assignments, quizzes etc have attached forums, then these discussions might also appear here.

Needs more thought.