I have a theory.
My friends and I have put much thought into this.
I believe that Xenagos (and possibly Ashiok and Kiora. . .) will become gods. I know Xenagos will become a god, but there's the catch with Xenagos:
Bolas is on Theros.
If you have seen any promo/prereleased pictures of Xenagos in the sets "Born of the Gods" and/or "Journey to Nyx", in both of them you have a great view of his horns. They are very, very, very similar to Nicol Bolas' horns, and if you've ever seen the "Born of the Gods" set symbol, it's very similar to Nicol Bolas' horns, and has a perfect oval/circle shape in the middle that can easily fit the Gem of Becoming inside. But seriously if Xenagos becomes a god, planeswalker, and becomes allied with Nicol Bolas, he's gonna be all like . And that's bad.