I don't think Dany can ever rule the seven Kingdoms. She's too much of a foreigner and she's from a house taht was hated and despised by most of the Great houses. If she takes back Westeros it will be with blood and fire as her house words go. There is nothing the smallfolk and nobles will hate more than having their lands raized to the ground and having a foreign army on their soil. I'm pretty sure Jon's not going to rule since he's up north and now the nightswatch is reinforced with the knights and footmen from Dragonstone.
Rickon is unlikely, he's still very young and wild as we left him with Osha. What they're doing is uncertain but I can see him becoming a wildling. Bran, Arya, and Sansa can be dismissed fairly easily as well based on their locations and sexes.
If it were up to me Tyrion would rule. He is a capable leader as we've seen but the citizens of kingslanding hate the dwarf.
So I guess I'm gonna end by agreeing with Arya the seven kingdoms will likely break up into seven kingdoms, with Dany aiding the nightwatch and then returning to her empire across the sea.