HD Radio is encumbered by the lack of a published standard (it's all proprietary iBiquity stuff at the moment) and even after that standard gets published, there will still be IP licensing issues (iBiquity IP, the audio codec IP, etc)... Effectively, you'll be trying to make something with the same IP issues that prevent a DIY DD/DTS decoder from being built, but with a bunch of extra complexity attached to it (RF downconversion, OFDM demodulation, etc)
Though almost every commercial in-car/in-home HD Radio decoder is based on a chipset from TI - you might be able to find an evaluation board for it and hide it inside a nice case.
Personally, I have issues with patents and licensing and closed standards being used in public broadcast...