Mike, no universal carousel changers have been put on the market yet; they are all single-disc players. Dale alluded to Pioneer, and I could see Pioneer doing it first. Panasonic (parent company: Matsushita) looks to be firmly committed to DVD-Audio, so I don't expect a universal player of any kind from them any time soon.
I agree that Pioneer will probably be first to the shelves with a 'universal' carousel. Hopefully, we'll have other options from manufacturers--like Denon and Onkyo--that have single-disc 'universal' models.
Mike and Angelo, Kenwood released the DV-5900M 403-disc DVD-Audio changer a couple of years ago as part of its Sovereign line. I don't know if it is still in production, but that is the only hi-rez megachanger they have made. Around the same time, Kenwood released the DV-5700 carousel DVD-Audio changer.