One niche I think is severely underserved is like. A good guy who serves straight up classic villain aesthetics. Like someone who's refined, and cunning, always plotting something, and if the setting has superpowers, they got an 'evil' coded power... But their goals are those of a good guy. I don't think I've ever seen a character like that, unless you count Col. Mustang from the Fullmetal Alchemist anime/manga, who ticks at least a few of the boxes.
(If you know of OTHER characters who fit my description, PLEASE tell me)
Warrior princesses (or otherwise 'fighting refined ladies') -- Who aren't tomboys, and are in fact fully feminine coded, but can still kick ass with the best of 'em. (Princess Leia, some iterations of Zelda, Rarity from MLP in a way though she's not a princess, etc.)