Gematsu made me look more into Rhythm Heaven and I am now a fan of Marshal as character. Still largely "meh" on Chorus Kids, although I would love to see the sort of move set Sakurai would develop for them.
Shulk was considered to have "a decent chance" and was on a lot of wish lists and prediction lists from the start (I know he was on mine) but he wasn't considered a "shoo-in" until Gematsu part 2. His chances at playability in the eyes of the Smash community where steadily growing since the Nintendo Direct that debuted Little Mac though, as little things such as Monolithsoft tweeting Smash news, the debut of X/confirmation that it was a Xenoblade game, and hints from both of Shulk's voice actors started lending credibility to that notion.
I wouldn't say Isaac was a shoo-in. He was thought to, much like Shulk, have a decent chance at making it into the game but was in no way a guarantee. Issac had more support then Shulk at the start of Smash speculation but that shifted as time went on . Sadly enough, a lot of people made it an either/or situation with those two because apparently the game can only handle one blonde JRPG protagonist. I've always strongly supported both characters and Isaac is on the top of my DLC wish list at the moment.
The only characters that I would say were seen as shoo-ins prior to the official Smash 4 reveal that didn't make it in are one of the Donkey Kong duo (K. Rool or Dixie) and Ridley. Chrom is borderline, since he was heavily expected but a lot of people where very loud in saying that Lucina, Robin, a returning Roy, a Lucina/Chrom tag team, or just Marth and Ike were all real possibilities for Fire Emblem this time around.