The stuff about the lemon trees and the house with the red door, and Quaith constantly manipulating and helping her through visions before important moments in the books make it seem possible for sure, but they just haven't seeded any of that stuff in the show.Guys. I'm sorry. But. I figured it out. I really did.
Next episode, when Dany confronts Bran about Jon being Aegon and the true heir, when she doesn't believe him and Bran has to reveal to her something only she would know... He won't just tell her about a red door and a lemon tree which we see in a flashback of her childhood, which on its own will be enough.
He will reveal far more. While Jon is present, and maybe others.
The reveal is:
She is not Daenerys Targaryen.
She is just a blonde impersonator. She was raised to be married, to get an army, it was a long con. Even her brother knew. "You don't want to wake the dragon now do you?"
It was a trick.
She'll say she is a Targaryen. She survived the fire, twice. "It was blood magic. You burned your husband alive and the crone and the Dothrakis. It's why they follow you."
She can ride dragons. "You're their mother."
She can... take a really hot bath without feeling it. "No you can't. You know it."
He hands her a candle.
When she despairs, he tells her not to. He tells her she has found what she longed for "All the steps you have taken have led you here, where you belong... home."
That will make the GC leader taking the throne under the name of Aegon even more tragic. Sansa will know and tell everyone. When she marries "Aegon" it will make it even worst. Daenerys will be remembered as a witch usurper.
Edit: it also makes it NOT INCEST.
It would feel out of nowhere.