Stick with me on this one. TWICE says HD Radio iTunes Tagging lets listeners mark a song for future listening/purchase. The process is clunky — users have to hear the song, press a “tag” button on a special HD Radio, connect an iPod to download the tag metadata, then sync the iPod to a PC — but I imagine syncing will improve as the functionality matures (ideally, the HD Radio should wirelessly transfer metadata to a PC or a mobile device).
Usability issues aside, the idea of “tag-then-buy” could extend to audio books. If publishers and radio broadcasters team up to air select chapters from audio books, HD radio users could tag the book for future purchase through an online retailer.
A system like this might be just around the corner. If the move toward DRM-free content continues to gain steam and consumers get comfortable with mobile-based buying, electronics manufacturers and content creators will look for ways to shorten the line between discovery and purchase.