There are many interactions between the separate modules you propose, and that might keep them from being separated cleanly.
You're right: I made it sound too simple. But with the new powerful gradebook (1.9) and conditional activities (2.0), a lot of the functionality needed to integrate the parts may already exist. Moodle is definitely moving in the direction of allowing complex activities to be built from parts. And I would say that any LMS that allows an end user to build the classic Workshop in a compositional manner has got it right.