I'm not sure the paytest packages went into any detail on this subject, and it's likely to be a DMG feature, so it'll be awhile before we see the finalised rules.
One option that occurs to me off the top of my head: For NPC classes, use the base classes.
Basically, if you're creating a non-heroic NPC, choose a reasonably-appropriate PHB class for them, and then give them all the basic features, but don't assign them a subclass. That will give them a general skill-set, without the more powerful or specialised options provided by the subclass.
This seems good.
although in most case I will just note the skills and proficiency they have and call it a day.