Yeah, I think Metal-Kitty's picks are pretty solid. There's a bit of me that wants to quibble and play with Pinkie's, Spike's, AJ's, and Derpy's roles, but then I think about them in other positions and I don't really think there's a better way to do it. Unless you make Fluttershy
the Engineer (the nicest character with the nicest class, "pets," cowardly playstyle which can go ham with a certain loadout, etc.) but then that rearranges everyone sooo, yeah. Metal-Kitty's probably got it as close as you can get.
Have any of y'all read any fics about other alicorns (or other "mystical" MLP creatures) representing other elements of the world in same way as Celestia, Luna, etc.? I've kinda been thinking about young Celestia's & Luna's friends and I'm wondering if I should think about any more of them as also eventually becoming future alicorns. I was curious if there was any fics out there (or any fanfic groups) that have good examples of "cosmology." I'd be only using them as inspiration, of course. ;)