I think you need to distinguish between AM and FM HD Radio. AM HD is dead, and was dead-on-arrival. If people have a hard enough time "decoding" an analog signal with their ears through the noise and variable propagation of AM, do you think radios will be able to decode a digital signal? Sure, the audio quality of AM HD is better than traditional AM radio. I have no AM locals that run HD, but I have heard bits and pieces of AM DX from my (quiet) home location and the difference is amazing. But when you consider the basic impracticality of it, it's useless and actually destructive to skywave reception, which some people still actually enjoy. I know when I had my Chevy Malibu (a "quiet" car on the AM band), I would sometimes tune to 990 CBW, 850 KOA, etc. when there was nothing on my local NPR stations but jazz or Garrison Keillor. That became much less convenient when WMVP started broadcasting HD at night, or those in the 1100's and 800's set out on their campaign of mutually-assured signal destruction. It used to be that 1100 - 1130 were the clearest, strongest HD signals on almost any radio: 1100 WTAM from Cleveland, 1110 KFAB from Omaha, 1120 KMOX from St. Louis, and 1130 KFAN from Minneapolis. Now they all run HD (or at least did), and all are hopelessly unreliable at best on anything but a fixed, directional setup.
On FM, well, for purposes of full disclosure, I'm a DX'er, so HD Radio is a bad thing for my hobby. However, the situation here is not nearly as grave as in major markets: there are local HDs on 89.9, 91.3, 92.9, and 100.5, the adjacents of most of which I can only really tune in weak signals on my XDR-F1HD, an excellent tuner which would never exist were it not for HD Radio. The programming on the local
HDs is pretty useless: the two MPR locals (92.9 and 100.5) don't multicast, even though 100.5 is the News outlet of MPR and would not be harmed at all by reducing their bitrate for a much-desired service such as The Current, 91.3 does but airs what appears to be a parallel stream to local 89.9, and 89.9 airs the only "unique" stream, an alternate 24-hour classical music service. So I don't see it being adopted up here, and the way the existing HD stations currently program contributes almost nothing to local radio listener's choices or enjoyment. And it blocks eight adjacent channels most of the time
(although KSJR often finds its way onto 90.1, sometimes even with HD)
In major markets, FM HD COULD be of benefit by increasing listener's choices. The only problem is getting it into cars, which I think are one of the few viable markets for HD radio subchannels. Many of the HD stations from the Minneapolis - St. Paul market decode on any given summer night here in Duluth using my trusty XDR-F1HD and rotatable outdoor FM yagi, and through that I can see the potential of HD. KTIS 98.5 (Christian, a format apparently very popular with the young adult female demo) now offers three alternate programming choices, including a stream of their AM talk programming; KNOW 91.1 offers 24-hour BBC World Service; KTCZ 97.1 offers an acoustic sub channel; KQRS 92.5 offers classic country, etc. I would assume reception from these stations is reliable in cars in the Twin Cities area. If HD Radio has any chance of succeeding, it is by lobbying auto-makers to include HD Radio in their base models and not as an expensive option.
Also, more choices is a much stronger selling point than better audio quality; if anything, consumers have shown that they are perfectly content with lossy audio files. This extends to other media as well; how many new TVs do you see that are capable of displaying HD but are used exclusively to display SD content, even if there's a simultaneous HD feed?