Or does he keep the tradition of Targaryen incest alive?

Now it's pretty obvious that Jon's not interested in any big leadership positions, but being king of the seven kingdoms is a pretty hard thing to say no to. If I am rightfully the heir to the throne and all the perks it contains, is it possible to walk away? I feel like Maester Aemon at some point mentioned walking away from the crown, and I really need to see Jon drawing parallels to his uncle's? great-uncle's? predicament.