Personally, I'd like to see at least the Udemy wishlist feature with a small icon (a heart for example) over the course image in the course catalog. You click it and it turns solid and the course is added to the user's wishlist.
Also, in my profile you have a "My wishlist" link listing those courses. Something like "My Courses" but only the courses that user has selected.
In addition, I'd like to run promotions based on the user's wishlist. For example, "This weekend, buy any course in your wishlist for half of its price". We cannot target particular courses because every user will have different courses in their wishlist.
In the backend, the administrator should be able to see some statistics or a list (a rating) of the wishlisted courses, thus knowing in what topics the users have interest but haven't purchased yet.