All HTC Tablets launched after September 2011 now can be unlocked officially
According to an update on HTC Developer site’s boot-loader unlock page, all the HTC Android devices launched after September 2011 are unlockable. They have even mentioned to update accordingly to reflect the same in the coming weeks.
They also assured that they are continuing to work on the models launched prior to September 2011. If you own one older device then you are requested to check back often for status of your device.
Android Central has even verified this with HTC Vivid which is even not included in the official list and another device which is also not included in the list is HTC Rezound.