I've seen no confirmation nor any design art that would give me any confidence about Kotarou .... but then we have no idea what they have planned after the Evangeline arc. I'm kind of ambivalent about him but he is important to the Kyoto and Festival arcs and it would be a shame to cut him (or those some version of those arcs).
EDIT: d'oh... ignore my first sentence. I just spotted him in an early release photo..... I'd say that's a pretty good sign he'll at least make an appearance and they do have him centered in the pic with all the girls.
