Are we allowed to express predictions in this thread, based solely on the show as I haven't read books?
edit. Ok read the OP and it says speculation from non book readers is allowed.
My end game theory is very simple, now that the arc's are coming closer to an end. I've wondered the point of the white walkers for some time, and the king. I've been rewatching and I firmly believe that the scene from season 6 where Bran sees the first white walker being created.. isn't actually the first white walker. I believe that in this scene, the white walkers were defeated thousands of years earlier by the children of the forest and men together. The man who is turned into a white walker is likely some kind of hero or Azor Ahai from back then and he was created then as the Night King to control or somehow oversee the white walkers.
Fast forward to the end of this show, I used to think that Jaime or someone else would be azor ahai and there would be some kind of twist at the end. I no longer believe this to be. I think enough twists have happened, the cards have been dealt and the landing gear is down so to speak. Safe landing is in sight, with some knee jerking at best. My guess is that John (Aegon) really is the the prince that was promised, azor ahai as everyone has been predicting. There will be some turmoil between him and Dany.. duh, but in the end the two of them will win the war. John will be set to sit on the throne and rule.. but he can't ... John kills the Night King, and there is nobody left to rule and control the white walkers and wights. John will be informed that he must be converted to the new Night King in order to restore balance to the world and "protect his people".
The show will end with Dany on the throne, heart-broken, pregnant and dragon glass being pushed into John's (Aegon) chest, final scene will be him opening his eyes as bright blue ... black screen.... credits.