Okay, I reworked the 3DS roster, and I think it works much better this way:
Blue Borders: Starting Veterans
Green Borders: Starting Newcomers
Yellow Borders: Unlockable Veterans
Red Borders: Unlockable Newcomers
If you want to know what those twelve icons below are, they are one of two things: Either additional characters I haven't predicted, or minus that, DLC (which we now know is going to be a thing). Me, personally, I chose the safe minimum and selected four characters: Blaziken (to coincide with the release of Pokémon Omega Ruby/Alpha Sapphre), Captain Toad (for his titular game), Bandana Dee (Kirby's Canvas Curse), and Rayman (just because he was advertised).
However, the eight blanks below can be anything you want it to be. Me? I'll just throw in the likes of Snake, Dixie Kong, Krystal, Hades, Black Shadow, Reyn, Isaac, and Takamaru; you know, the strictly fan service characters.
The Wii U setup I established previously is still preferred, though replace Jumpman with 8-Bit Mario.
Edit: That turned out great. The last one looked too much like an eye-sore, but this one actually looks like something I'd see on the 3DS!