You know, I'd be very much on board for this idea, be it in the show, the books, or the comic. I mean, I loved the Cake Twins when they first arrived, and I get a warm feeling every time they're on screen. What's to say they can't have one for the royal couple? They'd be doing these two a favor, seeing as those two were just dropped on us in the Season 2 finale. Also, who wouldn't want to see Twilight become an aunt?
And best of all, Hasbro could market this easily for the little ones. It's the best of both worlds, really.