Right... Leave it to Apple to write a specification. That thing is going to last for 5... 4... 3...
The article was written on 2017-08-29, almost a month before the official release of 10.13 (2017-09-25). Plenty of time to change our minds! Even the author says:
A future update to macOS High Sierra will allow... If that is before or after the official release of macOS High Sierra is not known.
Not too reassuring...

But after that it states, in the Update section:
The configuration is stored in: /var/db/SystemPolicyConfiguration/KextPolicy
I have a "virgin" 10.13 VM where nothing has been ever installed, not even the updates. Or I could create one from scratch. It would be worthwhile to test this location after the installation of VirtualBox, to see if the DB has been altered or not. Either there, or somewhere else in the hard disk. But I can't see any reason to store that information in the NVRAM, it would simply fail on a VM.