Consider a community of “experts” on some topic. Experts would like to post articles or questions on this board, to be discussed only by the other members, who are also experts. For this part, they can use any reasonable traditional message board software (with membership restricted to experts).
Here is the new part.
For each topic opened by an expert for comments by other experts, there should be a “shadow” topic automatically opened for comments by “the public”. Say, the expert’s topic is visible in the top (or left) half of the screen, and the shadow public’s thread is visible in the other half.
The idea is to keep the conversations among experts unencumbered from all the “noise” often generated by non-expert posts, while still allowing visitors to argue with each other about the discussion the experts are having.
A reader should easily be able to choose whether to view ONLY the experts’ discussion, or to view both. Searches should also allow this choice.
A related scheme exists at some news sites, where beneath every article there is a comments box (disqus, etc) for readers opinions. However, this is only one layer of comments.
In principle, the idea could be extended to more than 2 layers (imagine professors as the experts, grad students as semi-experts, undergrads below them, and finally the general public at the bottom). However, obvious practical constraints would need to be observed, in going beyond 2 layers.