In a large market, HD has a chance of getting minuscule ratings. In medium and small markets, you can attach a translator to your HD, and create a new analog station.
Depending on the geography, and ducting issues. Some of these stations show some success, or serve a town with a format that can take some points from a competitor without investing in a full signal.
Other than that, HD is useless at this time. It will take the support of vendors, and the public education to be viable.
Also licensing, and equipment costs will need to come down for smaller markets to adapt. Keep in mind, it took analog FM years to be accepted by the public (and the decline of AM).