A few weeks ago I would've said SMT X FE but......I guess I can't now

Zelda will most likely have dark elements in it as well

Probably XCX or Fire Emblem IF, Pandora's Tower was quite dark, under appreciated game imo would like to see another like it.

Don't know for sure. There was a ruined city and darker elements in that trailer. If it's anything like Persona, FE, or SMT, it'll be dark.

We'll never see Nintendo make a Bloodborne by themselves. Hell, even their Western games like 007 and Perfect dark were tamed down. Nintendo doesn't make games for western teens and adults. They make them for Japanese people and western kids. If they get older gamers outside of Japan? That's just a bonus.

Splatoon looks pretty edgy.

Xenoblade X I guess

I would like to see Metroid with a Dark Souls type vibe to it... An alien world that is cold and unforgiving, you're crash landed there and your only hope of getting off the planet is to destroy an ancient evil that decimated a long lost civilization. Your ship would be the hub, like firelink shirine or the nexus.  And as you explore you unlock more shortcuts around the seamless world map. Something like that. It would have to be 3rd person too because the first person thing was alright but 3rd person suits exploration a lot better.