"We’re thrilled to announce today that software updates to support bootloader unlocking will begin rolling out in August for the global HTC Sensation, followed by the HTC Sensation 4G on T-Mobile USA and the HTC Evo 3D on Sprint. We’re in the testing phase for the unlocking capability now, and we expect it to be fully operational by early September for devices that have received the software updates. We'll continue rolling out the unlocking capability over time to other devices as part of maintenance releases and new shipments."
HTC's plan for enabling the unlocked bootloaders gives them a bit of wiggle room: an August software update for the HTC Sensation in Europe, software updates for the other two devices "follow" at an indeterminate time, and then it won't be until sometime in September that HTC will release the actual unlocking capability. Fortunately, the company promises updates "every few weeks" so we'll have a chance to see if they're able to keep to this timeline.
HTC seems to be taking a slow and steady approach to the whole process of updating software and then unlocking bootloaders. It's actually hard to fault them on that given that the policy puts them at odds with the carriers -- let's just hope that those "maintenance releases" for other devices come sooner rather than later.
Source: HTC on Facebook