I was going to mention finding it odd that two characters in a row have had "Hermit powers," but the 17 lasers screenshot likely just deconfirmed Kasen. Unless ZUN and the others making the game are fine with using a character who is in the background, despite how odd that would be one some stages.
Several of the Touhou 13 characters are on the roof of the building in the background, including Seiga, who Kasen considers an enemy. Then again, just because Kasen has a rivalry with Seiga doesn't necessarily mean Kasen won't be playable just because Seiga won't.
And now that I look at the tapestry thing from the announcement video, I think I see what might be four oni attacking humans. I haven't seen Suika anywhere in the stage backgrounds.
And every one of the fighting games so far has introduced at least one new character. 3 Introduced 6 new characters (who were never seen again, like most PC98 characters), 7.5 introduced Suika, and 10.5 introduced Tenshi and Iku. 12.3 was an expansion to 10.5, so it doesn't count. We can be sure that we'll be getting at least one new character, so it wouldn't be surprising if Kasen and the uknown fourth oni deva were in this game. What better way to end their mini religious war than to have everyone unite againts a common enemy?