Elma
Chance: 55%
If we go by Sakurai's previous habits, then timing is on her side. Her game came out just around the timeframe Sakurai typically uses to draft characters in (it came out a few months before DLC wrapped up in Japan and about three in the west), and since XCX is one of the Wii U's most notable entries it does stand to reason he'd give her at least a look. The character also has a lot of tools to draw from that would make her a unique addition to the cast as her ability to both dual wield guns and swords aren't shared completely, her arts lend well to special moves, and with her Skell she has an easy Final Smash option that Sakurai can draw from. Tie that in with the possibility that the Vifam model's gun is similar to her (and other) Skell's, and I feel she has a pretty good chance behind her.
With that said, she's not the only one who could be considered from her game. Cross, while they're pretty much a viewpoint character in story compared to Elma (who's much more important), they are required for sidequests which make up a good bulk of the game. Additionally, they also have access to every weapon in the game including Elma's, which means they have a wider pool to draw from if Sakurai wanted to explore it for the character. As a result, Cross could be picked over her due to their own presence and the options they provide, though the fact that they're not as definable as Robin or Corrin does mean that they could just as easily be overlooked themselves.
All in all though, she's an overlooked character that has a pretty good chance in her own right. If Sakurai is looking for a character from the 2012-16 timeframe, she's one of the characters that would stand out from the era.
Want: 90%
I played XCX, and everything about her looks like she'd make for a fun character. Dual wielding guns and swords, a fast playstyle, great arts, a great design, and the ability to use a mech. All around, she would be a blast to have in the game.
Nominations: Lycanroc x5