If you want a destructible level, go play Teardown. Making BeamNG have fully destructible environments would bring everyone's computers to a crawl.
the feasible way to do this, and the way RoR did it, is with physics sleep. basically, if you have bridges, fences, etc. which so long as you don't touch them, they have their physics paused, so you only have to simulate the meshes (which could also be unloaed after a certain distance)
Not to mention that jBeams are awesome for simulating Steel and Plastics. But it's not really useful for simulating concrete, rocks & wood. I think the dev said they have the idea of making road signs, traffic lights, and other misc street items physics objects. No idea how far this is or if it will ever happen. Right now I would rather see more competitive AI so the world can feel more real before adding more sandbox flavor since the cars are already fun enough to smash (and you can make a house out of concrete slabs if you want and crash into it if you feel like)
