I want to know your headcanon with the Doctor, Derpy, Dinky, and Sparkler. For starters, here's mine:

12th incarnation Doctor Whooves (he regenerates into a pony)
From Gallifrey
Meets Ditzy/Derpy and has adventures with her through Time and Space and something happens causing Ditzy to age far less.
They fall in love with each other and get married [insert D'awww here]
Later they have kids via genetic loom (Time Lords are sterile) Sparkler first then later Dinky
Both Dinky and Sparkler are brilliant Time Lord/Pony hybrids that later travel with their father when they're older.

Debating with each other is also fine as long as you don't attack others with hate or anything else. I want to keep this civil. Begin!

Doctor Whooves isn't a Time Lord, he is just a time keeper. He is married to Derpy. Derpy seems to be a bit out of it, but she is a lot more intelligent than she looks or acts. It's like my portrayal in Learn to Fly, only with a less interesting back story for Derpy.