Well there are two types of doing 3D.
A. Full 3D worlds. C2 isn't strong with this due to it's presentation of level editor integration. The level editor system is very 2D and no serious easy to to do 3D.
B. Which I think can be added easily and has very fantastic benefits for 3D. Are to use 3D objects in place of 2D sprites. no camera roation. but they offer excellent animation, rotation, and provide object angled depth to a 2d world.
New Super Mario world, GTA China Town Wars....
heck even then you could probably still do some major hacks to C2 editor and do a 3D environment, but it wouldn't be the strongest.