mm.. i know a few thing about 3d modeling and how it can be used on osu,
i guess not every map will have dancers, only new ones
first you´ll need a ( example 100 frames animation [some engines work with this style]) and... frames 11 - 20 are a jump, and like storyboard, and using the bpm, in something like a storyboard editor, using the function "jump", will make the dancer jump, so the other frames could be used for, another dance moves like, 1 - 10 hands up, 21 - 30, get down, and thats not a freaking difficult work at all, and you´ll have the freedom to make custom dances, but you´ll not be able to make custon steps ,
this kind of system, doesnt need bone system on the 3d model.
it will need only 1 animation because the player will have all the steps loaded, and i guess it will lag less than have separate files
about the luigihann method, i dont believe it will work, or, it will work, but it wont be good - looked
ahh another thing, it CANT BE RENDERED!, it will look like 2-D image.
i hope this help