A bit of speculation, but considering you can see Unzan in the intro cinematic, i think we can count on Shou, Byakuren, Miko, Futo, and probably Seiga to be in as well. You can pretty clearly see all them and Reimu in it. This does make me wonder if that would put a potential 12 characters in it (although 13 would make it match the game number and allow for a surprise. just saying) with 4 characters per faction: 4 for Shinto (Reimu, Marisa and prolly Sanae and one more) 4 for Buddhism (Ichirin, Byakuren, Shou, and prolly Mamizou), and 4 for Taoism (Miko, Futo, Seiga, and prolly Yoshika)
also: Crossing the screen in Marisa's Broom Charge is fun.