* No intersection needed, it's better to limit the plugin to one 3D file + texture per "3D sprite" object. Usage would be mainly as the gifs i've posted in this thread.. Very very simple objects. They act and behave like a sprite but can be rotated in all diretions that's it.
I think intersection is the wrong term - true 3D always needs a depth buffer because it needs order-independent overlap. For example two 3D cubes next to each other cannot simply be rendered one after the other like everything currently is - you need a depth buffer to resolve the overlap in perspective.
* Transparency not really needed.
Your own rotating coin and playing card examples use transparency! Besides, in my long experience, anything along the lines of "that's not really needed" turns out to actually be needed (perhaps by other users than yourself), who go and file bugs saying that it doesn't work right and asking us to fix it.