I feel fairly confident Sakurai would put his own twist on Shantae's moves, instead of replicating how they work as closely as possible. I say this because of how he's handled transformation characters here. In Smash 4 it was believed transformations were removed simply due to 3DS system limitations. Yet even though there was nothing stopping him here, only Pokemon Trainer got it back. Heck, he even went and made Zelda further distinguished from Sheik. Because of this I feel he wants Pokemon Trainer to be the sole user of that playstyle; with the limiting factors from Brawl removed it would just lead to a crazed arms race for anyone else to try and replicate that, with those having more or less transformations instantly being better or worse than their transforming competitors.
I see Shantae's transformations being included as part of her base moveset, with the dancing used to buff certain parts.