Imagine the sexual fetishes that would arise! What horrible unspeakable things would people do with a new appendage! Disgusting
sounds like someone is having aspirations of draconian quality. i see a fallout with the heart theory though. with the possibility of heart disease in humans anyway, you would then have multiple ones to worry about. however if when one failed you wouldn't bleed out into yourself, it would be convenient. possible benefits of each are outweighing the drawbacks here though. i vote yes to all. call up the Genetic Engineers
as for uses of a tail. the list could be deemed endless depending on how much control you would have over it. with little to no control it would be utterly useless, whereas you could move it with full mobility, well no need to reiterate.
Well I would assume we would engineer out any disease involving fatty deposits from the blood clogging arteries.
I wouldn't want a tail. My grandfather sort of had one. A bump was growing on the end of his tail bone and it was really bothering him. When he was getting it removed a really long hair uncoiled.
Retractable claws a la Wolverine would indeed be awesome. How about enhanced endocrine glands that could make morphine, so you'd be immune to pain? Or methedrine-like substances for when you're fighting?
I would just engineer the brain to not feel pain on a unpleasant biases, rather on a emotional neutral biases where one could ignore it easily if needed.
Adrenaline works fine enough in most cases, it just a matter of making sure the mind is stable under that kind of pressure and does not panic.