Moos can be used to implement various sorts of interactive learning environments, not just sophisticated text-based virtual classrooms. MUDs are places for self-directed learning, learning that blends work and play, that often looks chaotic but that is uniquely effective. It allows users to navigate a historical area and to interact with objects and artificial people.
Interactive exhibits are one direction to go.
More interesting are structures activities where students have to do something, cooperatively. First of all, one could consider every MOO as an environment which teaches about itself. Some do it better than others. Hopefully, MOOs will grow into more than self-centered constructivism.