OK - I am going to subject you all to my crazy prediction again. While I LOVED the episode last night, something felt a little unsatisfying about it this AM that we literally have been worried about the White Walkers since season 1 and finally the living battle them and they die without us even knowing what their purpose was. Were they just pure evil? I don't think so...I think that's what the writers want us to think, but GRRM is very political and supposedly the Walkers are supposed to be a metaphor for climate change. Let's remember, this isn't some devil that was created at the beginning of time...the children of the forest literally created the Night King to help them against the humans. GoT is a series which literally ties so many loose ends up - certainly the important ones - and I just can't accept that the White Walkers are done and gone without us ever knowing why they were marching south for the first time in 1000 years.
I think over the next couple of episodes some weird stuff is going to start happening - and it will be clear that the Lord of Light is behind it. In a song of ice and fire, there is no longer ice. So fire will reign. Perhaps crops are going to die, perhaps stone men are going to start showing up in Westeros, or perhaps more undeads like Beric are going to be around but in a bad way. By the end of this series, Bran is going to go back and figure out why the Children created the Night King...and determine that for the balance of humanity they need to be created again. First thought is Bran becomes the NK, but I think he's too important to the living for memories so he'll stay the 3 eyed raven. One of Dany and Jon will become the new NK (or NQ), and due to the prior NK's trait of being impervious to fire, my current money is on Dany (believe Jon burned his hand in season 1 or 2).
This is probably crazy and out there but just seems like it could be the crazy twist we've all been waiting for. Finally, I have a theory on who will be a co-conspirator in this NK or NQ creatio - Lord Varys. Mel predicted he'd died in Westeros AND he is the most unabashed hater of the Lord of Light due to what happened to him. I can see him be the one pushing the dragon glass into Dany or Jon to make the NQ or NK and then die immediately after. A final sacrifice by Varys to save humanity slash combat his true enemy - the Lord of Light.