The more info that's revealed, the more it seems Okina HAS to be in the next fighting game. Her lore establishes relations with Miko, Kokoro, Kasen and Byakuren. Her age puts her on common footing with other long-lived fighters such as Mokou and Mamizou. She'd have choice words for Sukuna and Sumireko, whose incidents threatened Gensokyo's stability from within and without, as well as with Reisen, who fought another such outside threat. Being a god of outcasts, hidden things and discriminated people would make her sympathetic to Koishi. And her rivalry with the Tengu would give Nitori a good reason to fight for her allies.
Being of similar stature to Yukari, she'd probably be the next-to-last boss. I'd like to imagine she'd put on a Noh-inspired tournament and her stage would be a theater with all the other 2hus in the audience. The winner of the tournament would be selected to fight against another threat to Gensokyo, which would be the final boss.
Plus her EX theme is just too killer.