This is probably a long shot, but what happens if you take the IONVMeFamily.kext from High Sierra and put it in a Sierra install? Does it enable other drives there, or is the kext incompatible?
I'd check myself but I don't have an NVMe drive yet. Just wondering if it could work, as I'd like to remain on Sierra until High Sierra final release is made public (though I have installed DP1 just to see if everything is still working).
Send me the zipped kext!
By the way, what about Plextor M8Pe? My Sierra install committed harakiri, so I might try High Sierra now.