7. The Dragonriders
"The dragon has three heads."
This has been the key takeaway from Daenerys' vision in the House of the Undying, and it's very much believed that it means there will be three dragonriders, as opposed to just being a reference to the Targaryen sigil or the fact Daenerys does indeed have three dragons.
It's easy to see why: three dragons, three people to ride them into the Battle of Ice and Fire. They're expected to be a major part of the fight against the White Walkers, and Dany cannot ride them all herself.
Because of R+L=J, Jon Snow has long been theorised to be one of these three riders, and that's only intensified now that we have official confirmation he is indeed the son of Rhaegar Targaryen. The vision itself backs this up: Rhaegar appears along with a mysterious woman, and a reference to blue winter roses, which heavily connects to Jon and talk of his lineage.
So it goes that Daenerys and Jon will end up fighting alongside one another, after the truth comes out about his parentage, atop two of the dragons, with a third still to be revealed (the most popular theories on that front being Tyrion and Bran).
There could, however, be a wrinkle in all of this. Qyburn and Cersei are working on a plan to kill a dragon - albeit a very optimistic one - and Daenerys' dragons do make her more powerful than anyone else, if she were to really unleash them. Killing one off - likely either Viserion or Rhaegal - is now a genuine possibility, which throws a big spanner in the long-believed three dragonriders theory. At the same time, it does mean you could have Daenerys and Jon ride dragons without the need for a 'Tyrion is a Targ too' reveal (although people have been known to ride dragons without definitely having Targ blood).