I think it make no sense with the upcomming gpu render systems.
Take a gtx 590 and you are 500 times faster as one arm system.
Also a modern i7 2600k is about 50 times faster.
Arm via WM8505 Linpack Test 1-1.25Mflops
i7 2600k 8,500.09 MFlops
GTX 590 2488.3 Gflops
ARM processors are considered to be the most widely used, and by a very wide margin. But they are mostly used for energy efficient and low/medium computing power applications (mobile, embedded), not for high computing power like photo realistic rendering. However ARM cortex A9 series is supposed to scale up to 4 cores at 3GHz for server use. I heard Dell and IBM are planning to produce such servers in the future but AFAIK such chips (4 3GHz ARM cores) are not available yet.