in my opinion, everything is already there that is necessary without assembly wbs
In my macro stuff I'm moving Parts and placing Parts in Parts. I have found that if there were locks on the properties of a Part it can be used as an assembly. Part would need to have a placement offset X,Y,Z added to it for positioning so it's rotation could be around it's own axis. Assembly doesn't seem all that difficult if you just think about the act of locking some axis or restricting movements inside a Part.
Assembly storage data and all the extra bits I know little about, I would give way to Zolko experience in this area for sure. I think we would all like to have some kind of Assembly without adding too much.