It's kind of odd, given how Funko Pop ran for a long time basically maing immobile vinyl things known for being large bulbous cavities, that this has never really been attempted. But I guess that's the tricky thing about shells in general, because the sheer size alone is prohibitive for anything above a Core class (and maybe even then). POTP's take might be the main way to get it to work, size included. And y'know, paired with the notion of Transtectors, it kinda does work -- them leading with the Metalhawk shell and then making a Metalhawk was a pretty good turn of events.
In the "this just doesn't play by the rules of general retail" sense, it's perfect for a HasLab. Just don't know if any of the characters really have either the following or the cool factor that the previous HasLabs have done, to garner the kind of buy-in it would need.