So far I still hold on to the belief that most veterans for this upcoming Smash won't have their models/designs drastically changed from Smash Wii U. I'd probably expect them to look a bit more detailed this time around, but who knows. Of course, veterans with complete redesigns such as Link are the obvious exceptions.
Now, that raises the question of what characters besides Link will get redesigns. Personally I nominate the Villager getting their New Leaf designs over their City Folk ones for this game.
Either way, I honestly feel that for this game they'll likely stick with Smash 4's "artstyle," so to speak, considering the majority of Smash fans feel that it's a happy medium between 64/Melee and Brawl's styles. That is the reason why I believe that development-wise there will be miniscule reason for cuts from the roster.
It's incredibly likely they started the game as soon as the DLC was completed, or possibly earlier, and just used what was already built for Smash for Wii U, with some veteran updates of course in terms of moves, designs, and costumes (for characters like Pikachu and Jigglypuff for example). So similar to how assets are reused from Mario Tennis Ultra Smash into Mario Tennis Aces, the very same thing most likely is happening here.
It's only been two years since Nintendo stopped supporting Smash for Wii U with content. People are going to reasonably be expecting these characters to return. Otherwise fans might end up recommending the 3DS version.
It's kind of process of elimination here. There's no way they starte an entirely new Smash game from scratch immediately after the last game was released in 2014, I mean they did with Melee, but that was a much smaller game, and there's no way they could have done it in time for a 2018 release if it the characters were made from scratch in 2016.
That's not to say every character will return for sure. Maybe Wii Fit Trainer, Shulk, or Corrin will be absent. Who knows? But, I think it's very bold to claim that there will be cuts at this point.
I really wish people would just wait for more information before talking about cuts and debating whether or not it's a port. Though it's pretty obvious this isn't just a Deluxe port. If it was they would have a title for the game.