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This is a "Wild Mass Guess" entry, where we pull out all the sanity stops on theorizing. The regular entry on this topic is elsewhere. Please see this programme note.
Most of the original characters in the fic, minus the Mean Six themselves, are actually Expies of canon characters.
While Flathoof is of course fairly obviously an Expy of Big Macintosh, which is acknowledged in the fic itself, the other characters all have some very striking similarities, if you really think about it, to other canon characters:
Lockwood is an Expy of Derpy Hooves. He is a pegasus, and has a gray coat and gold eyes, and while his "official" career is a landlord, he seems to get around more as a social paragon. He knows everypony worth knowing. Derpy, on the other hand, is a postal worker (in-fic at least) who, in Chapter 23, reveals that she knows where everypony in Ponyville lives without any need for an address.
Tick Tock is an Expy of Doctor Whooves, though only in personally, profession, and manner of speech.
Briarthorn is an Expy of Braeburn, as the two have very similar habits of rapid-speaking, both serve as tour guides for their hometowns, and they even have similar colorations.
Doctor Blutsauger is an Expy of Photo Finish, from his German accent to his constant wearing of goggles (though Photo Finish wears glasses). They even share a catch phrase: "Zee Magicks!"
The Mean Six themselves, of course, are all mirror-flipped Expies of the Mane Six, at least at first. Their own character development shows them to be much, much more than simply backwards copies.
Flathoof and Briarthorn were killed in the plane crash
We've only seen Applejack survive the crash. and there's no mention of the others (minus The Mane Six, Tick Tock and probably Shadowstep) surviving it. Shame, I 've always liked them.