Agreed on the topic of planetary status quibbling
I really don't care what we call a planet, per se. It seems to make sense to me to continue to call Pluto one for the sake of tradition. But "planet" means what we want it to mean. So if the astronomy community decides to stop calling Pluto a planet or to start calling KBOs over a certain size planets I really don't care. I look forward to being totally bored by the pages of posts it will generate.
On your idea of high-metalicity large bodies existing in the KB: I do not expect to find any such thing. If we do, then I will gladly say: "Gee whiz! You were right and I was wrong!".