I'm going to be the very, very, very small majority in my idea on who Azor Ahai Reborn is and more than likely is completely wrong because there's few connections to the prophecy and the character himself… Also, I'm REALLY, REALLY reaching here as most of what needs to be fullfilled needs to occur in the next book before it could be possible at all.
I think it's Rickon Stark.
For one thing, he's apparently at Skagos. So he's north of the Wall. "Skagos" in the Old Tongue means "stone". Viserion & Rhaegal are now loosed in the world, but I believe Rhaegal made his home inside a pyramid while Viserion is elsewhere. Lord Manderly has sent Ser Davos to retrieve Rickon from Skagos after Wex Pyke told him about his whereabouts.
What if Viserion arrives after flying from the East and befriends Rickon in the same way that Jon & Ghost are united with a bond. And begins to skinchange into Viserion effectively "taming" him. Ser Davos arrives and things get heated near the water. Rickon is, by force, thrown into Davos' ship and Viserion in a fit of rage attacks and sprays fire around the ship but Davos and his men somehow "slay" Viserion as he falls from the sky leaving a fiery spray above with his blood falling in a trail behind him. Rickon within the heat of the moment tries to skinchange into Viserion and brings the dragon back to life on the land.
Rickon would then be amidst salt (the sea surrounding him) and smoke (the fire Viserion sprayed around him still smoking from the boat itself). Viserion would be "awoke" (brought back by Rickon skinchanging to help him) from stone (Skagos meaning 'stone' and is the land Viserion's body fell on). And the blood in the air amidst the smoke in the air would be a "blood star" of sorts.
And in doing so maybe some sort of inner magic is uncovered inside him and Davos realizes he's the real Azor Ahai? And in the final book, the Others are invading Westeros and Rickon returns with Davos, retrieves the fragmented Lightbringer from Stannis' dead body as in Viserion's final moments is used as the sacrifice to complete the sword. Rickon then becomes Azor Ahai.
Again, a ridiculously long stretch and reach for that one… but with George R.R.'s writing style for "surprise", it wouldn't shock me in the least for this to come out of left field and happen. Rickon has been left out for such a very long time, his character needs to have some sort of higher meaning in the end… Everyone else has served a purpose in one way or another.