I've touched on this elsewhere, but here's the crux of the problem:

Racking servers, even if they're cylindrical, is actually much easier than building an entire real-time image rendering pipeline from scratch.

The chassis that we co-designed and had made works out to a few hundred dollars per machine, since we aren't buying in giant quantity. When you talk about servers that run 24/7 and cost between $5k-25k per box, that's not the dominant expense by any measure. It's also been picked up by some other companies to use, which is always nice to see -- we aren't keeping it as a proprietary solution, anyone can buy it from our vendor.

Either way we decided to go, we would still be solving both the image rendering and machine racking / operation problems simultaneously to different degrees. As it sits now, we have about 4-5x the number of infrastructure and imaging engineers as we have datacenter managers / technicians on staff. As it should be, I think.

This design decision is actually part of our advantage, in that it allows us to deliver more functionality to our customers at a lower price per unit on the backend. There's always room for improvement, and we continue to iterate on it -- some day the Macs will probably be gone from the datacenter, but only when it's the right move to make.