havocthecat posted about a plotbunny. I've had this plotbunny for a while but am working on WAY too many things to pursue it.
In Pete's World, 10.5 assumes the name "John Foreman," taking the fake surname of his granddaughter, Susan. 10.5 and Rose eventually have a kid who has a kid named... Susan Foreman.
Through a strange series of events, the Eleventh Doctor and River Song wind up getting a distress signal from Pete's World in the future. Something is very amiss. Wee!Susan is in trouble. Cue some sort of Kal-El thing wherein she winds up being taken into the regular universe. The Doctor is not crazy about the idea of bringing up Susan in their chaotic existence, and River agrees, saying that having the TARDIS for a third parent led to brainwashing and danger for her. But, the Doctor has an idea...
He sends River alone back to London, 1948. There, he knows a certain grey-haired gentleman had landed temporarily, and there he has River bestow upon another TARDIS dweller the wee!Susan. "This is your granddaughter. Take care of her."
"But who--"
River winks at him and points to another police box. "Who d'you think?" She looks the First Doctor up and down. "You've always had the best ideas, and you'll continue." He's shocked when she plants a kiss on him before scurrying off to the other TARDIS.
"Didn't have to kiss 'im," the Eleventh Doctor grumps.
"Oh, yes, because cheating on you with yourself counts as cheating." She rolls her eyes. "You care to tell me about this Rose Tyler person?"