I'm not sure what's going on "under the hood". To get multiplayer to work, it could be a few simple switches here and there in the code. To have complete multiplayer however, you'll have to see the PC models in the 3D world. The ones currently in the game are stripped down versions, with low-res skins. A simple barebones patched *.exe would also require you to download the 200+ MB PC models in their original form
Another reason why the PC models / 3rd person camera was removed was probably the models sucking up heaps of RAM. Most people don't have high-end systems. I would have been happy with having the option of deciding for myself, instead of it being totally removed.