IBOC is claimed to make AM sound like FM, but 36kb coded 15kHz audio is full of artifacts to a discerning ear. Mine isn't, but I worked with MP3 (a different coding scheme) with someone who is. We had to get that up to 128kb before he couldn't hear "flanging".
The real push behind this is the transmission equipment manufacturers, and Ibiquity, who see a gold mine in the wholesale replacement of existing transmitters, and much upstream studio equipment.
The other pusher is large networks of FM stations, including Clear Channel, but perhaps more so, NPR. FM IBOC can be subdivided into multiple channels, allowing a single station licensee to serve two or three market segments. This is being tested on air as we "speak". The scuttlebutt is that it works acceptably, although my golden eared friend would probably yodel his lunch. My guess is that if, and it is a big if, IBOC catches on, there will not be an increase in audio quality, but in quantity. And that is a reaction to the competition from satellite radio.