I'm still wondering if Bode's Law plays into the definition in any useful fashion. Pompe's notion of "clearing the zone" seems relevant -- but assumes more or less "round" orbits, much as Countryboy points out the IAU insists on "round" masses. If we had a body the mass of Mars, in the shape of Clark's monolith (1x4x9) in the orbit of Halley's Comet -- well, it'd be interesting but it wouldn't be a planet.