A concept I always found cool on my head would have been someone that became a hero just so he could use his quirk freely or/and stop being spied by the government.
Someone with a deadly and dangerous quik like poison or explosions. The government found it early and after an accident forbidden him from using his quirk and treat him like a future villian.
The only way he's allowed to use his quirk and stop being under surveillance is if he becomes a hero.
Quirks are about self expression and individuality and having someone that can only be his true self by being a hero would have been cool.
Honestly there's so many interesting things that were never explored.
When the majority of the population has some sort of Quirk, even if it's entirely useless, the whole heroes and villains dichotomy annoyed me, there wasn't a lot of ambiguity in morality.
Marvel, as it was a long-runner in this, went all over the map with this, with a whole cast of characters that ranged from always good, always evil, and everything in between, including a long arc (Civil War, the comics version) that stemmed over the debate if supers should register with the government or not, and there, supers were a tiny minority of the population.
In a world with so many Quirks, the idea of "all heroes are fully registered and licensed by the government" and "all villains are common criminals and ruthless sociopaths" didn't sit right with me. The closet we got to someone breaking that was Gentle and maybe Stain, and even then they still fit solidly into the villains category.
From what I've learned Deku does briefly drop out and become a vigilante for a hot minute toward the later arcs, but I don't think it really explored the concept of "hero does heroics but because he's not licensed he's automatically a villain". Hell, I think that Gentle started out that way--tried to use his Quirk to help even though he wasn't licensed, ended up making things worse, and got his life fucked over because of it.
That’s what’s funny about the 20 members of 1-A with rubbish powers. Given thought those powers can be deadly as hell. And there were enough of them where you can give them many reasons for wanting to be a Hero.
That was the problem with Class 1-B showing up, since already a third of 1-A had boring quirks, useless quirks, or one-dimensional gimmick characters. Tailman, Sugarman, Invisible Girl, and a few others were destined to be background characters from day one.