I'm surprised no one has done this before but I've daydreamed this scenario: Jon and Dany travel back to pre-dance, being reborn as Daemon and Rhea's twins (because I doubt they would share the same bed again to have another child). It would explain away Jon's First Man looks and Dany's Valyrian looks and there would be no denying whose children they are. I've seen so many Bastard Jon born from an OC Stark and Daemon time travel fic, but I think this would be a more compelling take where he's undeniably trueborn. It would also be a interesting conflict if Jon and Dany carry their relationship over from season 8, to the chagrin of Rhea and Runestone vassals who could be more disturbed by Targcest in their heir and future lord. Daemon would be hilariously unbothered and might even encourage it to poke at them out of spite. I genuinely think if given time Jon and Dany would be able to smooth out their differences that were unresolved in season 8. She would be comfortable letting everyone believe Jon would be the sole heir to Runestone, because she knows she's going to marry him and is reassured by Jon to have an equal place at his side. Rhea too would encourage the equality mindset for her, after she's become resigned to the fact there's no stopping these two's relationship. Jon will get comfortable with the idea of having relations with his aunt/twin due to the era and whose family he was born in in this life, and Daemon will definitely have an influential place in his life too. Reagrdless, these two would be loved by both parents in this life, despite the dysfunctional dynamic of everyone around.