In the last year many software companies (Autodesk, BlackMagic Design) released products that weren’t available for the Mac before I think about DaVinci, Smoke and others.
Adobe developed the Mercury Playback Engine using Nvidia Cuda technology.
Eizo and Nec 10 bit LCD monitors, Atto 6Gb/s SAS/SATA RAID Adapters and OWC 6Gb/s SSD.
Just to name some new hardware.

OSX do not support 10bit monitors this is a known software limitation.

PCI Express expansion possibilities are limited; two PCI Express 2.0 x16 slots and two PCI Express 2.0 x4 slots inside the MacPro aren’t enough.
Five is the minimum number six would be the sweet spot leaving room for future expansion.
two PCI Express 2.0 x16 (Two video cards as required for example by DaVinci)
two PCI Express 2.0 x8 (Atto ExpressSAS R680, DeckLink 4K)
one PCI Express 2.0 x4 (Pro Tools HD Native)

Many PCI Express cards require an x8 slot.
The Atto ExpressSAS R680 require it to work correctly and so does the Blackmagic DeckLink 4K

Apple keep updating processors inside the MacPro adopting multicore processors (12 cores in the last model); in this case real life has proved that more is not always better; many test have shown that with most of the software 8 cores work faster than 12 cores.
Adobe with Mercury Playback Engine has delivered a technology that is really a game changer; unfortunately it uses Nvidia Cuda technology, and Apple has removed the Nvidia Graphic cards from the MacPro custom options on its store. You can still buy the Nvidia Quadro 4000 outside the Apple store but is not officially supported by Apple.

When major software companies finally released a working version of their software for OSX there is no Apple hardware to use them at their best.

In any case the possibilities that Apple could deliver a better MacPro are still higher than Microsoft to release a half decent OS.