i replied to this on another thread. It's not hard to implement the problem is that it would lag everybody like crazy. When you paint your plane if you want others to see it, it has to transfer that info to all the players. So imagine you are playing and someone logs in, it will begin transfering the graphics to every player in the room. your connection would slow down right at the momentn you are about to shoot someone... not nice.
then it will also take space on your device to store all this info.
and many other small things. I have to see if there is a way to make it workable but so far not an option.