In fairness, the majority of my development time was spent on three things: 1) Creating the custom user controls (from scratch) to support the interface, 2) The database structure and verification routines, and 3) Manually typing out all the data by hand. None of which they would need to do since all those elements are already in place.
EDIT: To be clear, I'm not suggesting it would be an easy, fast, or even feasible thing for them to consider doing. Just pointing out that I don't see many parallels between me coding a stand-alone planner from scratch and them writing a planner inside the game.