Allow me to pick your brains a bit. This is sort of Smash 5 speculation, but...sort of not.
We have
,
, and
. One for each game since Melee, these are old characters - if you can even consider them "characters" in the first place - whom no one really expected for Smash, but have very important, significant Nintendo history.
So...who could be next in this line? Someone (or something) old, 80s or earlier, who we probably don't see in games today unless it's a cameo, but nonetheless was very important to Nintendo. I've thought about this for a while and even done some research, but I can't pin down anyone that I feel really fits. It can't just be a random retro character that didn't actually make a noticeable impact even though people may remember them and/or Smash acknowledges them, e.g. Ice Climbers, Pit, Little Mac, Takamaru. The closest I've gotten is Sheriff and Diskun, though the Japan-only nature of Diskun leaves me not confident in that.