Something something vampire badstuff Nahiri is Avacyn.
It's a hell of a stretch that works only because they're the only two female characters with an association with Sorin. Ugin's dialogue indicates that Avacyn likely predates the sealing of the Eldrazi, so barring further evidence, I'd consider the topic dead.
The theory that Nahiri is Avacyn could be connected to this somehow, but I'm not sure exactly how. Also, I don't think a Liliana of the Veil reprint is coming as Wizards said they had tested her for M15, and had been way too powerful, despite designing hate cards in Karns.
5. Eyeliner.