What proprietary hardware? There are 6 thunderbolt ports for expansion. The only thing I can see an argument for is maybe the dual GPU cards, but you can upgrade that too through thunderbolt.
Right now the GPU is unknown, but it's possible it may have a W9000 GPU at the very top end.
Okay. Maybe I should just list data instead of comments without researching. I actually have built several EGPU units for customers. Never for a desktop, always for laptops.
Thunderbolt 2 as a E-GPU solution to a DESKTOP is a joke. It's smart on a laptop, because even with the incredibly deficiencies you still get more performance from a GTX 560 TI than a good regular sized laptop.
But let's say you get past the power limit by using an external power supply to provide the power.
AND let's say you get past OSX's limiting GPU solutions via bootloader modifcations.
Thunderbolt 2 is just a hair bit lower than the bandwidth of to PCI-E
2.0 at 8 lanes.
Recent tests on let's say a GTX 690 (one of the fastest but not the fastest single card solution).
Testing on the GTX 690 showed that between PCI-E
3.0 16x versus the equivalent PCI-E
2.0 16x (
double that of thunderbolt 2) there was about a 20% decrease in performance. (The equivalent test was using PCI E
3.0 8X lanes which is a good alternative to PCI-E 2.0 16x.
Now you are saying you want to put a GTX 690 level card (remember high performance?) with the equivalent of PCI-E 2.0 8X? You are talking about taking at least a 40% hit on performance using Thunderbolt 2's MAXIMUM throughput. Given the fact thunderbolt solutions even when using GPU's under the max throughput there is still a considerable drop off in performance, you could easily be talking about 50% or great drop in performance. (usually I got a mininum of 10% drop off in performance using Thunderbolt
even when the GPU was under the throughput).
If you used dual card solution, you'd be stuck with a 150W power limit for both cards and single width slot cards using Sonnet Thunderbolt case.
Your best bet with a Mac Pro is to shell out the thousands of dollars they will be asking for GPU upgrades.
Lastly you want many different boxes sitting outside of the Mac Pro?
Optical drive (some people still need them in the professional world believe it or not)? Hard drives? e-GPU's (very weak)? Sound Card?
Again as a Workstation it' a joke, you'd be better served running a custom server for probably 1/5th of the price. As a ornament for looks in a professional environment, it's plausible.