HTC has updated their Developer site's bootloader unlock page, and the news is good:
All HTC Android devices launched after September 2011 are unlockable. The website will be updated accordingly to reflect this in the coming weeks. We continue to work on models launched prior to September 2011, please check back often for the status of older devices.
We've verified this with the HTC Vivid, which does not appear on the "official" list. Same goes for the HTC Rezound. This is a big step in the right direction, and HTC has made good on their promises. Thanks, HTC!
HTC Developer. Thanks everyone who sent this in!