Kirby and Zelda are two series that could easily have had eight or more characters by now like Mario and FE. In an alternate timeline, I could easily see us with Impa, BWD, Skull Kid, Marx, Wolf Link and Midna, Magolor, a Champion, and Susie. Sadly, both franchises seem to be stuck behind the invisible wall of, "Welp, I added all of the franchise's main characters."
I'm sure this wall will be broken down eventually, because it's even more ridiculous to predict that we're never ever getting another Kirby or Zelda character. Still, it'd be nice if Sakurai broke it sooner than later, because until he does, I feel like it'll be hard to make a case for the latest and newest characters getting chosen when the many that came before them weren't.