Yeah, but ice is a mineral, which means it’s a kind of rock. At the proper temperatures, of course. 
Oh no! Now poor little Pluto has to wander the Galaxy, homeless, with a sign reading “Will clean out your planetary neighborhood for food”. So what happens to Pluto’s family of satellites? Are they going to tag along as Pluto stands at the interstellar turnpike offramp with his sign?
Pluto knows where it’s not wanted, so Pluto and all it’s little satellites children will be heading off to a new star where it will be finally accepted and loved and given a rightful and joyful place in it’s new star system orbit - that’s right Pluto will be given a place in the Goldilocks zone, no longer relegated to just to wander the icy and rocky outer edge of our solar system. Pluto will be the cradle of a new civilization and will be in a much better place.
Great idea. But…What about asteroids a lot smaller than Ceres? Little rockballs?
It would take some getting used to to think of Earth and Ceres as sharing a major category, but I think that’s cool. Makes you want to learn more about Ceres, and make it a goal for a spacecraft visit (manned or not).
Rockchunks. Aside from Ceres, and arguably Pallas and Vesta, all of the asteroids are too small to be balls, and do not have a “planet-like” structure.
And, it turns out, Ceres probably has so much ice, maybe “rockball” isn’t the best word for it, after all.