Allow professors to require supporting and counter points as part of the weekly requirements
This may be difficult to handle qualitatively, but it would be nice to have the option to require that replies be supporting points and/or counter points. For example, if you require three replies in a week, you can require that one is a regular reply, one is a supporting point, and one is a counter point.
The most important one would be counter points, since that allows for critical discourse. It also pairs well with the other suggestion of allowing replies on counter points and supporting points.