Tbh as much as people hate the idea of adding new civs to Japan, I’m warming up to the inclusion of Emishi (not to mention Ryukyuans but I don’t need warming up to them, I’m already convinced I want them). The Emishi could be a cav archer civ representing the mounted warrior side of Japan that the current Japanese civ doesn’t: they could get Mounted Samurai and Samurai Archers, one of which could be shared with the team Genitour style to reflect how the earliest Japanese samurai descended from the assimilated Emishi who served Tenno and the Yamato who adopted their tactics.
Not to mention that the Emishi were ethnically distinct from the Yamato, so it’s not yet another case of 3K or the Burgundians.
If the Japanese campaign is based on one of the civil wars, the inclusion of Ryukyuans and Emishi would at least increase the opponent variety as they could be used for the southern and northern clans respectively (the culture of Kyushu had much in common with Okinawa, the bulk of Tohoku population consisted of assimilated Emishi, etc).
I guess Japan could make for a separate DLC, with two new civs (Ryukyuans, Emishi) and three campaigns (two new civs and the Japanese). For the Ryukyuan campaign I’d love to see something about the Wokou pirates and their escapades stretching from Korea to the Philippines.