I was led to believe the current problem with using SDR# or HDSDR (or a standalone application) to decode HD Radio is that the codec(?) is based on a standard format but altered in a proprietary manner, making the authoring of any plugins or add-ons a violation of license or intellectual property law. DAB and DRM are open source/open spec, so there are plugins and decoders all over the web, but Ibiquity is very protective of their format. Radio stations pay them gobs of money to license their HD broadcasts, and receiver manufacturers pay royalties.
Considering that the receivers really haven't come down in price very much, and most of the hardware implentations are either expensive car receivers or almost-as-expensive add-ons to existing car receivers, you would think they would either market them better or drop the costs of the equipment down to consumer levels, but when it costs USD50 for a Ipod-sized receiver you can take out on a bike, and all it does is HD, no MP3 playing, no AM, nothing, who except the blissful rich is going to buy one when you can take your existing smartphone and strap it to your arm and listen to your own personal songlist, or streaming broadcasts of loads of radio stations, satellite services, podcasts, scanner feeds, etc.
That said, there's probably someone laboring under intense flourescent lighting and Red Bull right now trying to reverse engineer the HD format and build a soft decoder. But it will be a tedious process--there'll be no one to bounce around the subject with on forums, no Sourceforge project, no public discussions or exchanges of information during the development process. The project would have be on the down-low, little or no support will be offered, the OS of choice for the initial development will probably not be a Windows OS, so you're going to be waiting for a port, if it happens at all. Sort of like DSD.