I will omit the USB 3.0 card and the GPU card, because those are available either way.
1. Black Magic Ultra 4k card (I have to get a $300 external PCIe enclosure to thunderbolt adapter....OR buy a new device that replaces the functionality, somehow. Taking this route, I will still lose money).
2. Pro audio card, this is used for ProTools and I cannot afford to buy a new one. So it goes into another PCIe enclosure ($300).
3. PCIe SSD (Velo x2), sure this can be omitted, but that means I can't put in SSD's, so I have to get TB based external SSD's or a huge RAID system with SSD's, which costs a TON of money. The 2x Crucial SSD's and the Velo X2 only cost me $900 total, giving me 1TB of space and amazing performance. My internal HDD's are used as backup devices and then I use external USB 3.0 hard drives to do daily backups of the backups.
Get where it's going? Thunderbolt is still very expensive. Enclosures are nonexistent. USB 3.0 is cheaper, sure. But you are not going to get the same performance of SATA III (RAID 0) or Thunderbolt 1 or 2 with USB 3.0
My OS drives, I omitted from this because the OS is on a super fast PCIe flash based device on the new Mac Pro...but come on, it will only be used for the OS and not for holding actual data like large video files, etc. How big do you think Apple is going to have the onboard flash storage? 256GB? 512GB? That's not enough.
I think Apple just wants the Mac Pro to be a device that's just a "head", ie all the connections need to be external either via gigabit network (which is not fast enough for certain things) or Thunderbolt. Also what will happen if we want to go on a Fibre-channel network? Will there be a TB2 > Fibre-channel adapter? And how much will that cost? $10,000?
The Mac Pro is like the Mac Mini, but much faster and with more ports.
Anywho, this doesn't stop me from doing work, I still have my trusty '08 Mac Pro until it poops out.
Hmmm... You seem to have more PCIe slots than I do...
It seems that what you're trying to do will actually be easier on the new Mac Pro than whatever you're juggling here now.
BTW, most are expecting the new Mac Pro to offer anywhere from 512GB to 2TB of BTO SSD internally (that performs at 1200MB/s). If that's not enough, Promise makes the J4 TB enclosure for SSDs for a reasonable $370.