IT works really well! Know why?
1. Starlight Glimmer - Hyper intelligent, Super good at magic, and in many ways a total spastic nerd who makes rash decisions = Twilight
2. Sunset Shimmer - She has a real small home town, home coming honest sweet heart with a stubborn attitude, is smart, but her intellect is not her best attribute = Applejack
3. Trixie - Boastful, center of attention, funny idiot = Rainbow Dash or pinkie pie
4. Bulk Biceps - He doesn't really fit in as well, but is basically a gentle giant. Plus would add good dynamic for diversity. More or less his gentle nature makes him = Fluttershy
5. Dr. Whooves - Not so much the pinkie pie of the group, but if they played his "he's the doctor" card just right during the right times, plus the fact that he's a boy, would add some good elements to the group as a whole. He could possibly be the more "flawless" one of the group, the level headed inventor / mechanical genius. Maybe play up the "I have an invention for that" trouppe to get the group out of an impossibly tough jam.
6. Inky Rose - She was never a major character, and we will probably never see her again, but a gothic Rarity with the personality of Maud Pie would certainly be interesting. It would play up the girly dress maker, and we would have our feminine character, but it would present young girls with a different kind of girly feminine. Not the frilly poofy pink lace and gowns kind of girly you see in the pink toy isle, but something new and unique that would show that just because your not the same vanilla brand of bright poofy pink dress wearing tea partier, doesn't mean your not "girly" as well, and that there are different kinds of feminine, much in the same way that inkey Rose's Gothic, black attire still makes her the same as rarity.