We have begun shipping the eGPU cards that we've been working on for years. (literally, I'm sad to say)
First proud owner has reported success, his nMP 6,1 is running 10.13.5 with no mods at all. And he will be installing Windows shortly and report on that.
Some quick notes for future customers:
1. Easiest to install the Nvidia drivers before you get the card.
2. Before install, type the following into terminal: sudo nvram enable-legacy-orom-behavior=1 (From Apple)
3. Plug the eGPU into the lower left TB port on the 6,1.
4. Connect a display directly to the properly powered eGPU. (all power pins connected)
5. Boot your nMP 6,1 and watch the display come to life.
Once you have it set up, you can just treat the eGPU as being part of nMP. Boot screens, boot picker, etc are on the eGPU display. A separate blog post will cover Windows install, waiting to hear from Customer #1 how his Win experience goes before I write it up.