The worst part of Pluto's demotion from "planet" to "dwarf planet" is the sheer disrespect toward what's arguably the most interesting planet that's not Earth.
The second-worst part is that we can't call this hypothetical trans-Plutonian planet "Planet X" anymore.
"Planet X" was used before Pluto was discovered. The X didn't mean 10. In fact, Pluto was thought to be Planet X before they realised it was much, much smaller than that.
The second-worst part is that we can't call this hypothetical trans-Plutonian planet "Planet X" anymore.