Of course, in that situation, the scene probably fits in 64 MB, so it's not really a limitation.

Unfortunately not, at least not for the real work type of scenes that you see in movies / cartoons. Textures and high-polygon models take a ton of space.

Depends. If you do 3D rendering with triangles and shaders you can divide your buffers into tiles based on storage size and stream vertex/shader commands.

This is actually how all modern mobile GPUs work and it's highly vectorizable. The partitioning obviously needs to know the whole scene but that's much more lightweight than rendering.

From what I've heard from my ex-gamedev contacts movies are heading that route in a large way because the turnaround time a raytracing is so long that's it's really hurting the creative process.