Okay so. If I were JYP, we have Twice who mainly has a cute concept even though they're slowly maturing, we have ITZY who is girl crush, we need something new for NMIXX. Since the company wouldn't want two groups to overlap in concepts. Now we could do girl crush like StayC but NMIXX pulls off strong concepts very well so it would be a waste.
From what I can tell from Dice and O.O it seems they're going for an experiential vibe ala next level and zimzalabim. But they're just not pulling it off. So I would give them a pop rock concept, not a lot of girl groups are doing them and I think it would be nice to see.
Not the most general public-friendly concept sure but not every concept has to appeal to the general public.