EDIT My threadripper build was poorly chosen for a lot of reasons so I'm re-writing.
AMD build would not work because it has no Thunderbolt and compatibility is largely questionable.
My final verdict? This isn't possible right now with custom parts. They don't sell TB3 supporting Xeon server grade boards to casuals like us just yet. So 1tb memory with TB3 and ECC means you have to get a workstation desktop.
We can get close but not fully the same.
Here's as close as I can get.
Hard Mode, True Mac Pro Equivalent (Mostly)
This stuff available on PCPartPicker.
PCPartPicker Part List
| Type | Item | Price |
|---|---|---|
| Memory | Crucial 32 GB (1 x 32 GB) Registered DDR4-2933 Memory | $175.00 @ Amazon |
| Memory | Crucial 32 GB (1 x 32 GB) Registered DDR4-2933 Memory | $175.00 @ Amazon |
| Storage | Samsung 970 Pro 1 TB M.2-2280 NVME Solid State Drive | $299.99 @ Amazon |
| Video Card | XFX Radeon VII 16 GB Video Card | $499.99 @ Best Buy |
| Case | Fractal Design Define XL R2 (Black Pearl) ATX Full Tower Case | $150.01 @ Amazon |
| Power Supply | EVGA SuperNOVA P2 1600 W 80+ Platinum Certified Fully Modular ATX Power Supply | $389.00 @ B&H |
| Custom | Gigabyte (Alpine Ridge Thunderbolt 3 PCIe Card) Components Other GC-ALPINE RIDGE | $59.99 @ Amazon |
| Custom | fenvi T919 for macOS PC WiFi Card Continuity & Handoff BCM94360CD Native Airport WiFi & BT 4.0 1750Mbps 5GHz/2.4GHz 3x3 MIMO abgn+ac Beamforming+ WLAN PCI-E Card （NO Driver Needed for macOS） | $59.99 @ Amazon |
| Prices include shipping, taxes, rebates, and discounts | ||
| Total | $1808.97 | |
| Generated by PCPartPicker 2019-12-25 20:28 EST-0500 |
This Motherboard
ASUS WS C422 SAGE/10G LGA2066 $760
This Processor
Intel Cascadelake Xeon W-2295 18C $1475
Total Price - $4035
Has advantages - Better processor than base model. In fact, you'll have to move up to the $11000 Mac Pro to get almost as good of a CPU and a better GPU. Better GPU than base model, better gaming than the Radeon Vega II but worse professional performance. Also takes up much less ram slots so you can upgrade to the full 512GB in the future.
Disadvantages - Less expansion since max memory is 512GB and not 768GB. Less support. Unproven Mac OS support.