One thing I've noticed going into Ultimate, but even as early as Brawl and 4 is that Sakurai is way more willing to give characters mechanics that don't fit into the traditional Smash layout of normal/tilt/smash/special/final attacks.
So you have things like Villager/Isabelle's pocket, or Robin having his ammo counts like Fire Emblem's weapon uses or Inkling's ammo meter or Shulk having Monado auras, or Cloud or Joker's meter mechanics, or Ryu/Ken's Street Fighter inputs.
Even back in Brawl you had Olimar's Pikmin and Lucario's aura.
DQ Hero comes with a fucking MP meter and a whole ass spell menu letting him use all kinds of shit that wouldn't necessarily be able to fit into a conventional Smash moveset without having to trade something out.
So I think going forward, we don't necessarily have to restrict ourselves to "how can we fit the character's signature abilities into 4 specials."
Even Doomguy could have something like the radial weapon menu from the recent titles.