"Ghosts," Harry said, his voice flat. "You mean those things like portraits, stored memories and behaviors with no awareness or life, accidentally impressed into the surrounding material by the burst of magic that accompanies the violent death of a wizard -"

"Why," I said to myself, "would you have to die to make a ghost? It seems completely arbitrary." But then I thought that perhaps death releases a huge amount of magic that can't normally be drawn upon safely.

But then I had this wicked awesome idea.

What if a Horcrux is the same effect, harnessed deliberately? That's why it requires human sacrifice -- the violent death of a wizard. A controlled ghost-making, operated by a wizard who remains conscious and alive through the whole process, can bind the mind into an object, arrange for contingent regrowth of the caster from the record... Yes. Horcruxes are ghosts created under controlled conditions.

Which in turn suggests that you might be able to make a dying person into a superghost (or maybe even an immortal living person). Kill them to make a horcrux, but make the sacrifice immortal instead of the caster.