It's hard to say for sure who will and won't be cut, there's so many factors. But I'd be very surprised if all 58 characters make it back. Maybe they'll consider DLC expendable? Maybe Square or Capcom decide not to renegotiate? Will some series be considered not as important and be the first cut due to time constraints (almost certainly what happened to Lucas, imo)? The clone corner was purpousley low effort in terms of development, but as we saw with Brawl it's feasible we just don't get them at all.
Link will probably get some updates out of necessity, so something like the remote bombs seems pretty feasible. Need to switch back to a non-gale boomerang. I think his gear in general will have lots of blue explosions. I don't think it will be a full overhaul, though, just updates to accomodate his game ala TP & Wind Waker did for OoT & Young links respectively. He will probably still keep the hookshot, for example, despite BotW not having one.
Other characters, its hard to say. Fox & Falco will probably get visual upgrades to match Zero, for example, but would anything require a move pool update? Probably not. Between Smash 4 & now, many characters either haven't appeared in a different game or have but haven't gained anything to necessitate updates.