Ok quick update from me -
Im using a 1TB OEM PM961 in my 6,1 with the normal sintech adapter.
Yesterday I swapped out my drive with my original Apple SSD and upgraded it to Mojave. I then updated to the 10.14.1 public beta with the new boot rom described above.
Today I swapped my PM961 back in and installed 10.14 release.
My PM961 has 2 partitions including EFI. One with Mojave 10.14 (APFS) and One for Windows 10 (NTFS).
Update 1 - After several hours of trouble free reboots into windows 10 and back to OSX as well as cold starts I started getting KPs out the ass. Literally had 2 in the past 5 min. I have no idea what changed but it appears the problem remains, sadly
Update 2 - Well this is exciting. I've always wondered if my LaCie Little Big Disk 1tb Thunderbolt SSD could take NVME m.2 drives. It came from the factory with 2 PCIe AHCI m.2 ssd. I've successfully transplanted my PM961 from the internal connector of the 6,1 to one of the slots in the LBD and both volumes are recognized and I can boot into both OSX and Windows 10 from it. Note: I did experience 1 kernel panic so far (it was the first time I booted the drive) none since. The first time I booted the nvme partitions were not fully enumerated. I could see them in disk manager and system info, but the volumes would not mount (greyed out) - around this time I experienced KP and after subsequent reboot all volumes mounted and so far works great.
Update 3 - Been quite a day. I reinstalled my original Apple 512gb internal ssd and moved everything back over from my 1tb NVME drive. I rolled up a DIY external bootcamp driving using a Samsung EVO 850 SSD and a cheap USB 3.0 enclosure from my local Microcenter. Works great, get around 340mbs read/write which is more than I was expecting. Boots Windows 10 ever so slightly slower than the NVME drive and I think it will work out fine. I just use bootcamp as a gaming solution for my Mac Pro - nothing mission critical. Getting the partition cloned correctly so it booted, but I got it done. So mission to move all NVME partitions to alternatives locations accomplished.
Update 4 - NVME and Mojave have not been kind to me. I've got issues with the 2 NVME drives over thunderbolt. Disk manager can't format or mount them half the time and I've been unable to create a raid 0 set with them. Again, could be the controller I'm using which was designed pre-nvme however I was hoping that pcie over TB would be agnostic enough to let them work. However when I hook them up to my late 2013 Macbook Pro running HS they work fine and I'm able to do partition, format, create raid volumes etc, etc - no problems.