Mario & Sonic Guy
Old rivalries live on!
If only people thought that way about the Zelda franchise, since Sheik does technically count as a 5th Zelda rep; despite being Zelda's transformation, Sheik does play like a completely different character, and doesn't suffer from the flaws that the Pokemon Trainer has.There was never any official franchise limit talk.
Regardless, 5 characters just "feels" like it's enough for Mario.