I know that this is all just wishful thinking, but I'm currently sketching out concepts for if Nicole and Tengu returned.
I don't even care about Tengu, but I do remember Gen Fu's ending, where he took Tengu's nose after he was defeated, to use its mystical properties to heal his grandaughter.
So I'm thinking Tengu should be wearing an actual Tengu mask to cover the fact that he no longer has his signature nose. Alternate, to remove the mask, and all he has is the nasal cavity, like phantom of the opera and whatnot. Or do tengu noses regrow? I dunno. But his look should be "updated" somehow to show how he was defeated during DOA2.
As for Nicole.....I'm remaking her from the ground up, based solely around her intro/win poses, and quotes. I'm even thinking of a new fighting style/moveset for her, rather than the hodgepodge leon/bayman set that was later tweaked for Rachel. They can't use Master Chief, or a Spartan, but maybe they could get away with using Nicole herself. (MIST got her like Hayate, turned her into a new human weapon by internalizing the mjolner armor, or incorporating it into more practical armor?)
Either way, I doodling concept sketches for new Nicole right now.