I totally called Kogasa returning as a midboss (though a dialogue-less one) and a character based on a jiang-shi! I don't think Mima will return anymore. In the past traditional SHMUPs (which means not counting Touhou 3 and Touhou 9), ZUN only reused two bosses at most.
I'm liking Yoshika already! Her theme is easily the best in this game so far!
BTW, I've encountered a bug. After beating the game once as Youmu on Normal difficulty, I started over again using Sanae on Easy difficulty. When I reached Yuykuko, I couldn't speed through the dialogues. Whenever I pause and unpause, there is a chance that the dialogue will scroll when I press the Z button, or maybe it scrolled by itself after some time had passed. Because it was too slow, I restarted the stage, only to get the same result. I changed to playing Reimu in the same difficulty setting, but the same thing happened. Finally, I played as Sanae again using the same difficulty setting. Guess what happened...
I assume that things will return to normal after I exit the game entirely and come back. I'll try it when I feel like it. Has anyone encountered this bug, though?