My outrageous prediction: John Snow marries Dani. (The show ends with the birth of their child?) This makes the show come full circle: Mad King (product of Targaryen inbreeding) -> shit happens -> Child Born (product of Targaryen inbreeding). As you mention, Targaryens marry siblings all the time. Who will Dani marry is a question the show openly asks us to ponder, and there's no obvious answer. There's no one in the pipeline to marry John. There's no one in the pipeline to marry Dani.
Dani will start to go mad like her father did. Tyrian will kill her, he and Sansa will take the throne together. Roll credits.
The dragon has three heads: Dany will ride Drogon, the black dragon. Jon, the White Wolf, will ride Viserion, the white dragon. And Bran, the greenseer, will warg Rhaegal, the green dragon.
That is cool. Would be hysterically funny to have somebody smart and creative enough to simulate the google car going up and down the streets or areas. Catching characters and such.
Game of Thrones season 7: Everything you need to know https://www.yahoo.com/news/game-thrones-season-7-everything-141619530.html