The problem with that is... I dunno, the fact that Horcruxes are Teh Ebil is sort of stressed heavily. I don't think it's just the act of killing that creates a Horcrux. I mean, if that were true, Voldemort would have a lot more than seven. And all the DEs would have a fair number as well. It's not just killing another, it's tearing out part of your own soul at the same time. Dumbledore seemed so adamant that it was such a terrible, terrible thing to do.

Now, mind, I think the phoenix has something to do with it. I mean, duh, death and rebirth. But I don't think it's a Horcrux situation. I think he'll find a greater power in death -- in a spiritual form that can't be harmed, that can't decay like his physical form was beginning to -- than he could maintain any longer in life. Like Obi-Wan said, "If you strike me down, I shall become more powerful than you can possibly imagine."