I would be shocked if Jon ended up sitting on the Iron Throne. It goes against everything GRRM has talked about and done in GoT in being almost an anti-LOTR. It's too easy, too simple, too cliche. Jon being half Targaryen? Neat, and has been set up since season 1. Job being the rightful heir? Neat, it makes sense especially given what book readers have said about even more hints and small details. However, Jon being a bastard that is the epitome of two of the most common genre conventions, especially of high fantasy, with the metaphorical Jesus character AND the one person destined and capable of overcoming the great evil that will otherwise destroy the world. I would be very disappointed, but I have faith that Jon won't win the war and then claim his place on the Iron Throne.
Maybe Jon survives the war, but Cersei backstabs Jon, and Dany gets the Iron Throne like she always dreams of but it costs her the love of her life (which I am not and was never a fan of JS+DT). But the show ending with Jon as king? I'd bet against it.