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For comparison, Ceres[1] has a 473 km radius and is considered a dwarf planet.

[1] https://en.wikipedia.org/wiki/Ceres_(dwarf_planet)

Ceres considered a dwarf planed because it hasn't cleared the neighborhood around it's orbit, not because of it's size.

I don't think the suggestion is that this object is planet IX, it's that this object provides evidence that there may be some other planet IX out there.

I think that 'clearing its orbit' standard won't survive. Say we find an earth-sized object out there past pluto, or say a jupiter-sized object around another star, the fact that their orbits are full of other tiny objects won't matter. If it is big enough, the other technicalities will fall away.

A rogue planet orbiting a galactic core, or massive BH, would still be called a planet despite in no way clearing its orbit of anything.

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