Am I reading this correctly and is this completely redundant? Or would something like, the technology is obviously there but nobody has done it qualify?

What is the lowest quality and/or permanency bar to resolve? E.g. would duct-taping a robotic snake to my buttocks count?

@MartinModrak No, it would need to be something controlled directly by the wearer independently from other motions/actions.

Something like a mind control prosthetic.

@KamalNdousse Then maybe update the question title? "Prosthesis" usually covers even completely passive devices. You also seem to imply that physical connection of the "tail" to the body is not required, do I interpret this correctly?