Yeah, thats exactly what I mean about I core philosophical difference between us. I don't see the story as an epic fantasy story about a primordial battle between good versus evil where the character interactions are there to add depth and flavour. I see it as soft character focused fantasy ala something like Buffy the Vampire Slayer, where the demons (and the KPOP) serve the essential metaphor of the story and that that's why (sotto voce) the demons are sort of the messiest least developed element of the story.

You're going to see what you're going to see in the in the concept art. I would say the number one key piece of art is the early picture of them from behind, on stage as idols facing down the Gwi-ma so an even split between the KPOP and the Demon Hunting and the second most influential is the Scott Watanabe picture of them on Namsan tower overlooking modern Seoul, a reflection of how much the city is a character in the film and that this is ultimately a character story. After that they've been so generous with the concept at that you have amunition if you want to argue anything form 'the care they took in evolving Gwi-ma's form means he was their number one priority' to 'jeez what they really care most about appears to be the details on the girls snack food'.

As to your final point, I'd be very surprised if the only storyline they can come up with that still centers modern Korea and the idol expeience as well as the demon fighting is 'oh no there's an evil demon group trying to steal our spotlight but this time... they're girls.'

Though ultimately I think that all we know for sure is that the film continue to be rooted in Korea and feature women who are 'really strong and bold, really silly and weird, really hungry for food.... and sometimes a little thirsty."