I'd love a "head" option for severing though (obviously it would kill the person mind you). Nothing gets the point across like a severed head getting thrown into a bar. As well as the ability to sever body parts from a corpse.
As for adding canvas functionality to body parts, I don't think that's necessary given the speed they deteriorate, and as far as I'm aware if you really want to display a body part somewhere long term, you'd want to do so by RPing some type of taxidermy and using a canvas item in the game for this (like people have been doing for ages).
I'd be a fan of adding a "display" option for body parts or corpses as long as they deteriorated at the several-day rate that a normal corpse would. Could prevent some of the somewhat stale body part displays around the Mix.
It would also be convenient if someone was able to just lob off someone's head and stuff it in a cooler as a way of preserving their head-based chrome until they can find someone to remove it, but I realize the amount of coding behind that would hardy be worth it.