I'm personally more "worried" about enemy variety than story. I don't really need a cosmic horror kind of twist to the story, but their previous games had some incredible enemy design and variety, which is something that I just don't think can be done if most enemies are humans for story reasons.
I imagine this is part of what motivates so many people to ask for a twist. Everyone was cool with Bloodborne back when we thought it was simply "Dark Souls with guns", because that came with werewolves and shit.
The most out there enemy we've seen is the headless, and, well, as interesting as the fight seems, and as creepy as the concept is, it's still kind of just a dude.
That claw enemy the player used the Evo 37 parry on in the TGS trailer was interesting, but it just seems to be a recycled enemy from Ashes of Ariandel. Or to be more accurate, they borrowed a Sekiro enemy for that DLC, as that enemy attacked far too frequently for the typical Souls moveset, it felt out of place.
When you think about it, regular humans is indeed a brand new type of enemy for Miyazaki games, as much as werewolves were for Bloodborne, but not as much in the context of "action adventure games", or even "ninja games".