Quoted from nman:
Heard an interesting theory that Bran might eventually be responsible for the creation of the Night King in the same way that his "visions" have already influenced the past in other ways.
Not sure if it will pan out but that would be interesting.
There is a therory on youtube that Bran is the Night King. He points to how not only does Bran have an impact on the past but the past can physically make contact with him as well. So the man he saw being turned into the Night King by the Children of the Forrest was actually himself in the future.... in the past. LOL
Anyway its a facinating therory and he has some interesting points to support it that I'm not touching on.
Part of the fun for me at this point is all the different therories.