No it’s not internal expandability. I don’t care that you think desk cables are ugly. Pros don’t have “desks”. The word “workstation” includes far more than the machine. SANS and externals RAID enclosures are the norm. Having an internal SATA Time Machine doesn’t make you a “pro”.
I’m willing to give Apple a pass on the single-socket design but only until I see the price.
What really breaks this for me however is the choice of GPU. It doesn’t matter how great of an AMD card it is because it’s an AMD card. No this isn’t a religious devotion to nVidia, it’s more about app support. Like it or not, Apple, Pro products outside of your own don’t Support OpenCL completely (or at all) but many of them have incredible nVidia CUDA support. Especially the Adobe suite, but there are others.
If we’ve learned anything about Adobe, it’s that they take a very long time to get these types of compatibility updates out and only put them in the most recent products (see: OS X transition, Intel transition, retina display support). Don’t expect miracles out of them.
When the Mac Pro launches (probably around Halloween) pro software will be running entirely on the admittedly beefy CPUs instead of the GPU (like it does just fine on a 15″ retina MacBook Pro with nVidia 650M).
So while AMD (and even the Intel 5000HD) cards may selectively beat out nVidia’s offerings on specific OpenGL benchmarks, none of them will ever have nVidia’s proprietary CUDA support. (I’m also not sure if the Intel 5000HD even has full OpenCL support.)
Of course OpenCL is the way of the future and apps should’ve started using it instead of CUDA back in the days of Snow Leopard, but they don’t yet. Maybe this is the only way to get The Foundry and Adobe to fully support it. For me, a Mac Pro is a machine you keep for 5 years though so I’m happy to wait until either an nVida version or OpenCL support from Adobe.