Tidus does throw me a bit as well. I mean, the only reason he would have would be to reject Jecht (if Jecht is now Cosmos), but he worked through most of his daddy issues at the end of his story in Dissidia. Soooo... Not sure. Unless it's really Shuyin on the side of Chaos, and nobody knows it because they look identical for reasons that still have yet to be explained.
Also, how the heck did I miss confirmation of Gilgamesh? LINKIES!