Well, here's who I'd think will appear in the game for sure. SPECULATION FUNTIME, GO!
Shintoist (sort of): Reimu, Sanae, Suwako, Kanako
Buddhist: Byakuren, Shou, Ichirin(?)
Taoist: Miko, Futo, Seiga
*Insert what ever else I may be missing here*: Momiji and/or Kyouko PLOX
Reimu & Sanae are a given, and Suwako/Kanako are Goddesses. I chose Shou and Ichirin because they just seem closest to Byakuren, in my eyes. Can't say for sure on Ichirin though. Murasa seems more suited, but... I can't decide. Miko & Futo just seem to make the most sense there, and Seiga seems pretty popular/important :V
Now, Marisa is in the game, and she's not exactly the religious type, as far as I can tell. Meaning there will likely be others who aren't, but maybe it's just because she's a protagonist. I would also imagine Suika, Iku, and Tenshi appear since they starred in the fighter games (though appeared in Double Spoiler). But with the game revolving around religious danmaku filled warfare, perhaps they won't.
If I don't get my Yuyuko, I will explode.
EDIT: Typos, because I like to rush things~