Nor did Renko, Maribel, Watatsuki sisters, Reisen II, etc etc :V
Depending on which speculation/theory is actually true (if any), Maribel's possibly been fought in an XX.0 game.
I'd be surprised if Kasen showed up in a game so soon. Her own manga series had only just recently begun. Her plot isn't even completely established yet from that series. The three fairies didn't get to be in a game until waaaay later, too. Of course, like the three fairies, I do expect her to show up eventually.
Now that I think about it, does Hetate even really count when considering this? You technically did fight her spell cards in a game (Double Spoiler when you play as Aya). Sure, it wasn't an XX.0 game, but it was one of the closest things, I think. This also applies to Iku, Tenshi, and Suika (who weren't listed)
....eh. Me personally, I'm expecting characters who've never been fought in any fashion before in a danmaku game (IE, not just xx.0, but also the shoot the bullet games). Of course, that basically means I'm 99% expecting all new characters. ZUN re-using a character as a danmaku boss in an xx.0 game is EXTREMELY rare. Off the top of my head, the only times a char's been used as a boss in multiple games is Cirno (2nd stage boss in the first game, a midboss in the 2nd) and Lily (who doesn't really count that much since she's more like a random feature in Phantasmagoria). And Marisa/Reimu being fought in one of the PC-98 games vs one of the Window Games, but I'm not sure if that should count either since it's... well, PC-98.
Outside of new characters, the only characters that haven't been used in a Danmaku game are Kasen (too early, IMHO), the fighting bosses (Suika, Iku, Tenshi. All 3 I'm not really expecting but I suppose it's possible), and some of the written-works-only characters, most of whom I wouldn't really expect to show up either (though again, it's possible).
In essence, if that character was a boss in a previous game, I'm not banking on them showing up as a boss in this game.
