I read this and could only think of one thing in regards to pegasus ponies mating with others. Wings would have to be a genetically dominant gene, because, to quote Rainbow dash, 'Only pegasus ponies can walk on clouds' Unless there was some 'it's magic, i ain't gotta explain this...' thing involved, which would be plausible but perhaps overpowered, then any ponies born to pegasus ponies that WEREN'T pegasi themselves would end up falling to their deaths as soon as the cord was cut. I mean the other solution is that they could be pegasus ponies that live on the ground (aka fluttershy) but if all pegasi come from cloudsdale, at least to begin with, then I don't know. That said, where on earth does scootaloo live? Hmm.. maybe pegasi come to earth to mate n have their children but then return to cloudsdale as some sort of rite of passage?