So, for canon!Billy/canon!Rapunzel, I love the idea of this happening post-Dr. Horrible Canon. (Because Rapunzel and outlaws is a canon thing. But not really because of that.) I don't know, I love the idea of Rapunzel helping him get over his guilt, but not....Over Penny? I legit feel like she'd respect that she'd always hold a place in Billy's heart, but she just has SO MUCH good inside her to show him and help him find hope again and a different way of making the world less of a mess. And Rapunzel would just love all of his inventions and potential and how smart and handy and awkward he is. Plus he would sing with her; major bonus to her. They'd probably be a pretty schmoopzy pair for a while, with less, if any, of Rapunzel's teasing, because I think that's what Billy needs post-canon and she'd recognize that. But then, eventually, if Billy seemed he could take it, they could have a nice little domestic relationship where they kind of poke fun at each other and point out bad ideas, but always support each other and know the other cares about them.
(Entry originally posted to my DW journal.)