I fully support the IAU definition of planet. What I disagreed with in their 2006 decision was to not make Pluto an honorary planet since, given public sentiments, I feel unjustifiable suffering was induced. The scientists would know the difference regardless so the only group it affected was the public whose happiness was reduced and sadness was increased and, philosophically, I cannot find a reasonable justification for it. A few months ago, Matt O’Dowd of PBS Spacetime regarded the idea of bending to public sentiments as childish but if the neurotransmitter math says the cortisol outweighs the serotonin and no superceeding reason can be found then it is imperative that suffering is minimized and happiness maximized.
In the end, the ontology of the universe does not provide us categories and everything is a blurry spectrum. We draw the lines and then believe they’re real when they’re not. What is real are what the lines attempt to represent so we should draw them according to moral law. Usually, this means in whatever manner minimizes suffering and maximizes happiness. However, there is another, more distant, way to define planet: the political definition. In relatively soon forthcoming posterity, there will be settlements throughout the solar system. Pluto will not nearly be among the first and will be centuries before an outpost is founded. Closer to home, we have large moons and large asteroids from our own moon to the large Jovian moons to places like Ceres and Vesta. While minor bodies will likely be outposts of large polities, a place like Ceres will likely be its own sovereign entity.
For space treaties, do we have different terms for Ceres, Ganymede, and Mars? It seems ineffiecent. For political purposes, they are all planets. Now, for large asteroids and the Jovian moons, it would probably make more sense to have them in a loose confederation but loose because of the lacking celerity in transit between them. Governance is very inneffecient if communication between Ceres and Vesta takes an hour each way. Also, bandwidth will be telegraph level over the radio waves. Each celestial body will have its own intranet where one can update your blog to your community or book a dinner reservation in an adjacent city but between bodies, it is going to lots of demand for relatively tiny supply. Movies and music and large media files will be transported in physical starships to be released months late at their destination. Hollywood will likely have its own fleet of starships just to haul media around.
In any case, Pluto’s planet status would be based on its population, social organization, and independence to be recognized by other planets. Charon may legally be its own planet or legally be one with Pluto. Also, the Jovian moons could be fully sovereign, a loose confederation, a tight federation, or a sovereign union and so could any other close bodies. All of these definition have the same thing in common: the benefit of humanity is their aim. If it is merely a matter of semantics, then words need to serve humans less than be held to have an objective meaning. Their meaning is to convey information for the benefit of humans and words’ meanings should be bent to humans’ welfare.