Switch for what? If they want to switch to Macs for render boxes, they're insane. They just made a deal a few months ago with Intel for a 1024-processor renderfarm (128 processors per node). We'll never see an 128-processor Mac.
However, I thought they already used Macs for doing the actual movie, then later offload to the Intel renderfarm for final rendering. Correct me if I'm wrong.