As the author points out, it's much easier to find 3 MHz of available spectrum in an ISM band than it is to find 20+ MHz. Yet even with the 20+ MHz needed for 802.11g or the 40 MHz needed for 802.11n, hundreds of millions of WiFi users are able to make their WiFi devices work, despite sharing the same spectrum -- with other WiFi users as well as with Bluetooth, Zigbee, cordless phones, baby monitors, etc.
The argument that tomorrow may bring a wireless application that is more beneficial is, in my opinion, a good argument for allocating even more spectrum for unlicensed ISM use -- not an argument for limiting ISM use to only those standards that are already established (WiFi, Bluetooth, etc.).
As for copy protection concerns, that is a good subject for an entirely different discussion about analog vs. unencrypted digital vs. encrypted digital content and the DMCA law...and why copying for personal use is permitted for the first two types of content, but not for the third (encrypted).
The reason for not using up all of the spectrum today is that tomorrow something much more useful may arrive that would benefit us a lot more than not having to run speaker wires. That is one reason. Next, consider that these wireless systems offer no protection from interference by other systems using the same frequencies. Beyond that, there is an interesting realm of copying concern, if we have a digital transmission of some copy protected program, and the transmitted version is not copy protected, we have just defeated the "copy police". I admit that is a stretch, but it could get some folks excited. To repeat myself, when the spectrum is all used up, it is gone, and they aren't making spectrum any more.
While there might actually be some value in wireless audio, using it just to avoid running wires is a terrible waste of spectrum. Remember that there is only so much spectrum, and when it is full there is no more room, and something loses. So yes, it is neat to be able to do this, but it does constitute a waste of spectrum.