Personally, I think Dixie will wind up with the same fate as the Inklings: They both have great potential, and good fanbases, but they are relevant enough to be saved for a greater hype factor for Smash 5. There's going to have to be some conserved momentum, and this ballot is being used for the future and the present. With K.Rool we've brought him back from the brink of oblivion, and that is definitely something to be rewarded with his choice as DLC establishing his return to the DKC franchise, while Dixie already returning means that she can wait. Add to that while I think there will definitely be a female Ballot character, I think it's likely to be extremely unique, at the least humanoid, and either from an un-repped or barely repped franchise.
Also, with that criteria, I would say an Indie character is not impossible, but would have to have some pretty high standards, and one of them is having an established legacy, which honestly Shovel Knight doesn't have, he has a single game with about 300,000 sales on Nintendo systems, which is smaller than even the niche first party characters getting in. While Shantae has 3 games and greater sales(still smaller than Nintendo characters, but the stronger relationship). Honestly both are unlikely, but I really wanted to put out some full thoughts on this.