Dany is definitely pregnant, and then not only is Jon the true heir to the Iron Throne, but their child would be next in line. Can Khaleesi handle that?
Jon will make it a point that he has no desire for the iron throne. I think it may add a little drama over an episode or 2 but the series doesn't have that much time for all that. They may kill one of the 2 off before they get married though and then the child would technically be a bastard which is Jon's worst fear. Hopefully there will be a small ceremony at Winterfell before the Night King gets there.
Or history could repeat itself it terms of Jons mom. And I agree, Jon has never wanted to be king. And ask yourself why Peter Dinklige has top billing all these years ?
Therein lies the drama, if/when he discovers his true lineage. Does he marry his aunt or does he let his child become a bastard? I like Tyrion, but wouldn't want to see him as king. He's better off behind the scenes, like his father.