does the bsp tree not act similar to a scenegraph? I'm not big on the bsp tree the engine uses atm, but a bsp tree could be a scenegraph logging which entities are in what leaf node. As well, with your pvs pre-calcs on map, most static entities like triggers, placed mines, can be determined near enough via the pvs. As well, can't you extend the pvs in runtime to allow attaching a list of dynamic entities to nodes, so only the entities attached to nodes in the pvs for your current location need to be checked for collision/interaction? Am I making too much of an inductive jump based on my minimal q3 bsp tree information?
My engine is using a quadtree based scenegraph since my game will be on a heightmap based terrain. Dynamic and static entities can be placed and test culled easily with the quadtree. As well anything close enough can be ruled out with early fail sphere-sphere checks ( using the non-squareroot version )