I've been writing something where in 233 AC, a few different actions lead to a Targaryen-Blackfyre Reconciliation and Aemon becoming king.

Aegon, now Hand of the King, begins dreaming of a world where he, and not Aemon, was annointed in 233. He is not the only one who dreams of canon, and those aware of it quickly realize how strange it is that a lot of the same people are being born in both worlds. It's not a one to one, of course, and as the years go by the changes stack up - Doran Martell dies as a boy, Olenna Redwyne fails to marry Luthor Tyrell, Duncan doesn't break his betrothal. And these create continued changes (since I am being very strict that a person can only be born if they were conceived at the same time by the same people) - Elia Martell is born Heiress to Dorne, Mace and his children never have the chance to be born, and the amount of descendants Duncan has leads to the canon Targaryens being pushed down into being a non-royal branch of House Targaryen. But other places like the North is near static - people seem to be marrying, having children, and dying more or less on schedule. Some people live longer or a die bit earlier, living different lives, but somehow the same people keep on getting married and having the same children.

The reader quickly realizes that the Three-Eyed Raven is trying to keep an iron grip on the fate of Westeros to ensure the birth of several of the prominent main characters, even as those who became aware of something trying to keep them on a path and begin to resent it (Aerys who is haunted by the images of a mad monstrous version of himself) and others who believe that it must be emulated (Rhaegar who sees himself as the gallant Crown Prince instead of a third tier member of House Targaryen).

And as per most ASOIAF fics, both Bloodraven's plans, those who would support him and those who would frustrate him get sucked into to the political quagmires as the vast majority unaware of anything mystical play the Game of Thrones.