It's like this. Modern astrology as a whole doesn't much trust science, and doesn't much like history. There are a few exceptions, of course, but most modern astrology is intuition based. There are some interesting studies out there about how informed intuition is better than uninformed intuition, and how often the 'highly intuitive' are wrong, but I digress.
I think it comes down to this: If it orbits in the sky and it is personally meaningful, then it's an astrological planet in modern astrology. That takes care of the Kuiper Belt objects, because you know that as they're discovered, each one will be the 'key' to someone's chart, at least per that person. But not everyone will use all of them. In another 20 years, I'd be surprised if new astrologers are using Pluto still because of its lack of planetary status in astronomy, but who knows?
As for the asteroids, it's taken as read that the IAU naming conventions are divinely inspired, so it comes down to personal meaning again.
And for some types of astrology, this will work. It will make people feel better, less alienated, justified in their alienation, understood, special, or whatever.
As chaotic as modern astrology is now, it's going to become even more personal, intuitive, and harder to share with other people. How can you? It doesn't have rules, and more planets and objects will make it less cohesive, less communicable to others.
Maybe astrology will take a dirt nap for another few hundred years after it gets ludicrous. Or perhaps it will be a personal and highly idiosyncratic pursuit, as it is now for many people.
It doesn't work with traditional astrological technique, because you can't leave out the planets you don't like or that 'don't speak to you'. You can't add in extras. We have rules. Modern astrology pretty much doesn't.
At least I think that's what the general consensus is, and how things are probably going to go. If you like modern astrology, use modern astrology. I think we who use traditional techniques get a little upset because you guys don't have rules, standards, or a cogent philosophy. But that's our problem. And no, I'm not being ironic.