Ice Climbers
As has been noted, the 3DS and possibly 8-player Smash were the reasons they were cut. Unless this is basically going to be a port and they intend to make the Switch capable of playing online vs. Smash 4 (which would require them to patch Smash 4, of course), those limitations are irrelevant now.
8-player Smash could still be, but it's kind of silly to let that keep the ICs out. They made it so Miis almost weren't playable in With Anyone online, but if Ice Climbers caused a problem, they couldn't ban them/limit the number of players using them in 8-player Smash? Not sure why that should be any more upsetting (I'm pretty sure people spend more time playing online than 8-player).
The Smash community really wants them. On the other hand, I think they have a non-trivial chance of not returning since I question how much appeal they have among the casual crowd. Since the Switch is selling well, Nintendo would prefer this sells over 13 million copies like Brawl, not 5 million like Smash Wii U, and that means going beyond the hardcore crowd that cares a lot about the ICs. But still, a veteran is less work than a newcomer.
Ice Climbers chance: 89%
There is some chance they decide people didn't really miss the ICs or they only have limited spots to expand the roster and they don't want to cut a veteran or there are other newcomers they prefer. But characters that were cut for relatively minor, now mostly irrelevant reasons would be the most obvious additions.
Ice Climbers want: 30%
I don't hate them, but I haven't missed them at all in Smash 4. I assume that they would be balanced to prevent wobbling (since Smash 4 had anti-chain grab modifications) which would make them less annoying inclusions. But I find Rosalina more to play as far as similar characters go. I don't find the characters compelling at all in terms of personality and their original game, but I get the desire to represent some old history (although that's also represented with G&W, Duck Hunt and ROB...) If I could have another newcomer, or add the ICs, I'd pick a new character. I'd also pick almost any other non-clone veteran over them.
Wolf prediction: 83%
This is a pretty bullish crowd, and any unique* Nintendo-owned veteran is going to get pretty strong numbers
*aside from his specials (which are still overall more different than Falco's), Wolf's move set is unique
Nominations:
Bayonetta x1
Concept: Custom moves return x1
Lucina x3