Dixie's far from a sure thing. There's no telling if Sakurai even knew about Tropical Freeze back when he was planning SSB4's roster. (There are a lot of major games from 2006-2007 with no representation in Brawl.) And even if he did know, that doesn't automatically mean he wanted to include Dixie as a character. Dixie was only ever planned as a tag team character in Brawl -- as soon as that mechanic was cut, so was Dixie. Maybe Sakurai doesn't think she warrants being a standalone character. Who knows. All I'm saying is that Tropical Freeze isn't necessarily some kind of benchmark. If anything, I expect the game's Donkey Kong representation (characters and stages) to end at DKC Returns.K. Rool is my most wanted Smash character, and I think his boat sailed long ago.
Unless he's in Tropical Freeze, we're gettin' Dixie. She was planned for Brawl, after all.