I think the same. I am extremely confident Bandanna Dee is going to happen. For Elma, its very suspicious that there is almost no Xenoblade X content in Ultimate yet a Mii costume, several tracks ans spirits for Xenoblade 2. If Elma is outright lacking a spirit in Ultimate, then I see it no different than the bread crumbs that made it obvious to everyone that Dark Samus was coming.
Dixie Kong is a huge name, but I cannot shake the feeling if she was being planned that they would have held off on showing off her spirits. However, as you said, she is a good candidate for a Lucas/Wolf/Isabelle type character which would lower the burden for the team. I wish I could feel more optimistic on Dixie Kong in general, but right now I already see the five slots as:
1. Microsoft newcomer (likely Banjo-Kazooie)
2. Square-Enix newcomer (likely Geno, could be Sora or a Dragon Quest character though)
3. Namco-Bandai newcomer (likely Heihachi, could be Lloyd)
4. Bandanna Dee
5. Elma or Dixie Kong (right now, I feel Elma is more likely due to the suspicious absence of Xenoblade X content).
Honestly, Dixie does have some merrits.
They might've just pushed her back into DLC development because making her a Echo proved to be out of character.
We also heard from Sakurai that Isabelle was once considered for a Villager Echo, but the body porportions didn't allow them to. And I guess overall popularity made them think Isabelle is worth more than being a simple Echo. In the end however.. after seeing Isabelle being played far more, there isn't much unique about her moveset compared to Villager aside from what we saw in the trailer. Literally everything else seems taken from Villager.
So if we consider that, would we really want Dixie to follow the same route as Isabelle? I personally think not honestly.
Now, we should also look at what we've gotten from the Smash 4 DLC, which is of course the highly requested veterans ;
. And only one of them, Mewtwo, is 100% unique. Roy and Lucas are semi-clones. Then there's
, and all aside from Ryu reuse assets from other fighters. It's been said that Cloud was based on Ike's moveset (as a base), Bayonetta was build from assests from Zero Suit Samus, and Corrin had Marth as a base. Of course all of them are unique, and only borrow the minimal, but fact remains fact... Only 2 of the DLC characters seem fully unique. And those are Mewtwo and Ryu.
So with that being said, Dixie might have a good chance, and her outcry was mostly as a unique character. Sure there where people who wouldn't mind her being a Echo, myself included after Chrom's reveal- but most of us want more out of her. Dixie can easily be build up from using Diddy as a base, and then implement DK's cargo element as a unique gimmick, as well as Peach's float (as a base maybe). So that could be the reason why her inclusion was deemed to complicated for Echo status, and otherwise not realisable just as Isabelle is (who I feel is far more cloney than the likes of Roy, Lucas, Luigi, Ganondorf Wolf, and Falco).
There's hope. We just didn't really realise it yet. Sure 5 spots alone is depressing, but it might be enough just for Dixie to make it in. If Rex was denied for example, there's a good chance they looked into titles before Xenoblade 2's release, and one of the biggest titles released was easily DKC Tropical Freeze. At least, on Nintendo consoles. Yes Elma also seems likely, a Square-"rep" is all but confirmed and Namco-Bandai might want a character in, but it would be weird if first party characters where totally skipped. She has a "hype worthy" enough gimmick or two to be hidden, with the Helicopter Spin and hair grabs, so that's a factor in her favor.