In all honesty after the hard push for "You ARE the NPCs" I don't see them pursuing the idea. We have story driven, merchant based, and random encounter NPCs in the form of non human characters. Bethesda has specifically went out of their way to not break the "everyone's dead or schorched/ you alone must reclaim the earth" idea and they're very unlikely to go back on that. Especially when they're still focusing on trying to help level and ease player interactions and community/faction building within the area. To be completely honest I'd be pretty upset if I had to deal with some rando human vault dweller NPCs a year in because they abandoned the HUGE basis that there wouldn't be any human NPCs. They just need to give us more NPC abilities and role playing tools.

That being said, there's definitely "soft maybe" precedence set for introducing humans later on through notes, and holo tapes. The first example is of course that outside of Vault 76 there is a note from scavengers who are scouting saying they'll come back soon.