Clearly, Scootaloo is a one-off clone of Wildfire created by dark experimentation by a rogue group of pegasus scientists seeking the extreme of where they could push the pegasus' abilities. However, Scootaloo was a failure of sorts, and so was palmed off to a orphanage.
Little do they know, that she has other aspects that make up for her lack of flying.
...Or not. But that gives me an idea.
Like the marks, I think they fit really well. Applebloom I'm kinda torn on, because to me she's always been more of a builder-repairer. Either that, or in my headcanon she's actually going to be Equestria's first gunsmith.