Quote is a character that is trapped in an interesting position: He's an important character in terms of being the protagonist of one of the very first games to start creating the Indie game boom, and he also does have some level of story with Nintendo, considering every game in which he's been featured (even games where he's just a cameo, like Blade Strangers) has appeared on a Nintendo console. Moveset wise, he has an insane ammount of options in terms of how to make the character playable, from his Level Up weapon system, his varied arsenal, to things such as how the Booster could be added.
However, he suffers from a big problem, which is a lack of a real popularity. Cave Story's prime time passed a loooong time ago, and I'm pretty sure a lot of more casual players don't really know about the importance of the character, or even know him at all. This, combined with an overall very silent community (compared to some other popular characters, at least), make the chances of him even appearing in the game not as great as they could be.
I honestly would love to have him in the game, Cave Story is a game that is very special to me, and Quote is probably my most wanted character in the game right now, even if I know his chances are very slim.