Except Sakurai had an article about exactly why the Ice Climbers aren't playable. He tried everything, even removing bones from them and removing gravity, so he said, to no dice. He only barely got the Pikmin to work and he had to cut their numbers in half and animate them like ***. I don't think the Ice Climbers are coming back for this installment, ever.
As for Snake, the whole Konami issue.
I think Ivysaur is more of a possibility than Squirtle, because Greninja
Pichu is definitely a possibility, especially if you throw in Plusle and Minun alts. He would be widely hated, as he's among the most divisive characters in the roster. I don't hate the little yellow rodent, because he was a secondary of mine in Melee (I played Pikachu and Bowser more). I actually wouldn't mind seeing him come back, but the fan rage could be too intense.
I would legitimately hate to see Young Link return. Sure, we have 3 Marths, but that's because they are different CHARACTERS. Marth, Roy, and Lucina. I don't need to see Link have three different iterations of the same character. Link, Toon Link, and Young Link. People don't like the idea of 3 Marios (Paper Mario) and he's frickin MARIO. Link shouldn't either.
Chorus Kids...it's possible. What with Gematsu being MOSTLY right, and Chrom was even considered at one point. But this had to be very early they had that information and stuff can change. Chorus MEN, rather, need to be a hell of a lot more easy to animate than the ICs, like Game and Watch simple, to be possible. Or use visual trickery to make one character appear like it's three
That said, if both pre-ballots (both marios in the data) are pre-ballot, I think Wolf, Pichu, and maybe Chorus Men take those spots. Then again we had NO INDICATION that Ryu was even planned before the data mine, despite being pre-ballot, so this makes Chorus Men's Gematsu status sorta irrelevant. I WANT to believe Ivysaur could be pre-ballot but I can't be too biased.