I'm not aware of any plans to add 3D capabilities to GIMP. Gimp is strictly a 2D platform.
You can simulate a few 3D effects in GIMP but that's about it.
A good 3D package needs to be built as a 3D package from the start.
For you to be able to render and/or animate in 3D, the image must be described in 3D so you'll need a package capable of handling that. Something like blender
Some 3D packages are able to take a 2D image and "extrude" the 3rd dimension but that techniques has limited use.
You may find these links useful:
link1 link2