[MAIN SPOILERS] Something everyone seems to be ignoring

Just because Jon Snow is now a legitimate product of marriage doesn't mean to say he is the 'rightful heir'. Rhaegar died before he became king, so his line was cut off. Viserys became the 'rightful heir' since he was the next eldest son of Aerys (if we ignore that he was usurped by Robert anyway). From there the next eldest child (Daenarys) would surely be heir, not the eldest living male relative (Jon).

Please correct me if I am wrong!