Huh, what's their reasoning? Like I said in my earlier posts, when you really analyze Elma's chances, they're actually pretty good. Only reason Sakurai would choose to omit her now is if he didn't feel like adding another Xenoblade newcomer at the time.
People are assuming that every single newcomer is going to be a fan favourite. And not even Ballot contender,s that's why very few talk about Bandana Dee, who was extremely popular and requested in those days, but they are bringing back character that were requested during Brawl like Skull Kid, even tho their support was weak during the Ballot they are practically confirmed due to the dumb forniture theory. People think that because they have added Ridley and KKR then every newcomer is going to be a character requested for ages, while they completely ignore the other fan favourites chatacters that are a lot more recent like Inklings and Chrom. Also they forget that Richter wasn't a popular pick, but being TP means that he had to be planned since the beginning due to licensing. He wasn't a last minute addition.
But they are wrong. There is no way that Sakurai is just going to do Ballot picks (especially because, from all the fan polls, there really aren't any clear top picks left besides Bandana Dee and possibly Isaac). I belive that is not how Sakurai picked the whole roster for a series of reasons:
1)Whenever a character was added due to requests, he outright stated it, like how he did for Snake, Ridley, Chrom, Dark Samus and so on. If every single character was like this he wouldn't have the need to state that every time.
2)The idea that "he already announced KKR and Ridley, he must have something big to top that!" is wrong. In Brawl he topped Sonic with Olimar, in Smash For he topped Mega Man, Pac-Man, Little Mac and Palutena with Robin and Shulk, and even with DLC he topped freaking CLOUD with Corrin and Bayonetta. He doesn't keep the most hype inducing characters for the end.
3)We have seen Nikki and the Badge Arcade Bunny as AT. That means that Sakurai isn't only looking to the Ballot for choosing what content to add in Smash, and that new games aren't completely ignored. X is extremely unlikely to be completely ignored, considering it was one of Nintendo's biggest titles on the Wii U alongside Breath of the Wild, which was derivative from the world building of X. Considering that they haven't shown anything from it, not even an AT, that probably means they are keeping it for something big...like a character reveal.
4)Sukapon and Ditto prove that Sakurai is also giving a second shot to old and scrapped ideas from the past. That's why I'm convinced that we are going to see the Chorus Kids being added (especially after Chrom was also brought back), and since it is extremely likely that Sakurai had considered Elma in Corrin's place for DLC he would have already some ideas to work with.
That is my personal stance on the matter. I'm sure that the next reveal will prove that Sakurai isn't just following the Ballot results, whenever it comes.