From what I’ve read, the morphing only existed in the first place because [Rare] had to save on RAM, so they re-used existing assets for Spinal’s enders. Now that RAM isn’t an issue, Spinal gets to be his own, complete, unique character.
“Patching it in” would first require they remove his current ender animation(s), animate 25(-100, if there is to be variation between ender level) transitions (this could be shortcutted), program the new ender animations to trigger, program and apply the RNG necessary for the morph, and go through more than a hundred different enders to balance what can come from where and how, while maintaining balance within context of his current kit, and adjusting where necessary. Then there is having to account for it in the lore. Why would a skeleton even be a shapeshifter in the first place?
Sounds like a whole lotta work to nostalgically pay homage to a cost-saving measure from a time well behind us.
EDIT: I know very little about programming, so I’m sure it’s not simple as I’ve described. Almost guaranteed to have missed several steps, and we’re already looking at a huge investment of time.