He’s the longest of long shots, as Khal Drogo has been dead for a very long time. Drogo’s death was not as central to the narrative as Ned Stark’s, but he has been six feet under for nearly as long. But if Game of Thrones were to break all its rules
and bring back a character who has been departed for years, Drogo could fit the Prince Who Was Promised build.
It's also only after their marriage that Dany came into her own as a character and leader. Drogo did wake the dragon within her and is indirectly responsible for her becoming the great ruler she is today. As for everything else involved, it's hard to argue Drogo’s prowess as a warrior. Before his death, he was planning on invading Westeros and that invasion would likely include ending the darkness that will envelope the country. He doesn't have a fiery sword, but he does a dragon that is named after him, Drogon. Fire-breathing dragon beats fiery sword in GoT rock paper scissors, last time we checked.
Drogo really could be the perfect Azor Ahai -- if he wasn’t also so perfectly dead.