A new node type would only be required if permissions were different. I don't see this as a "proliferation". You are proposing a similar "proliferation" of new "forum type" nodes which have /more/ fields than a nodetype and would require re-implementing the permissions structure that is already nicely captured in nodetypes.
I like the idea of not always having to add a new root node type for each "section". Granted, you were thinking mostly of new fora specifically for the sake of having different access permissions, where two extra nodetypes might be required for some sections.
But this is such a fundamental change, that I'd approach it in phases and look at implementing a forum as you've described without simultaneously taking on fundamental changes with permissions (which need to be done very carefully because they are too easy to get wrong -- as we've done several times not too long ago).
Anybody could work on this.
But you are the only one who was added to gods with a mandate to work on it (patch approval).