...Well, um...
Guys, you remember that discussion or two a couple of pages back about Shantae's moveset-based transformations possibly being to hot for the 3DS to handle?
Well, I finally thought of a counterpoint.
A moveset-based transformation
does exist in the game with no problems, and it's right here. Bowser's Final Smash, Giga Bowser, reverts him to his feral state from
Brawl - including giving him his moves from
Brawl.
His entire moveset changes in some way when he uses his Final Smash.
My theory on why this works and why Samus/ZSS and Zelda/Sheik don't is because Giga Bowser isn't an implicitly separate character anymore like he was in
Melee;
he only even shows up when Bowser is around, so his model and moveset are pre-loaded whenever Bowser is around. Samus/ZSS and Zelda/Sheik, on the other hand, are separate character data entirely and have been since
Brawl and
Melee respectively. The 3DS' choking might not be because of model- and moveset-swapping, but because of having to call a bunch of character data that wasn't originally loaded into the match while unloading the previous character, possibly several times in the same match.
With this in mind, a transformation-based Shantae might be able to work the same way that Giga Bowser does: her other models and moves are already loaded and can be swapped on the fly, just not usable until the right conditions are met. It's certainly possible with a little bit of techno-sorcery like making her alternate models loaded, but invisible until the transformation calls them.