Not long ago we got to share the great news with you that HTC formally announced they would no longer be locking the bootloaders on their phones. We have a screenshot of a user getting on HTC's tech support chat, and getting confirmation that HTC will indeed be including the Sensation in this new policy of "unlockedness". However, there are a couple of caveats. Because HTC had already locked the bootloader on the Sensation before they altered their policy, apparently, it is a difficult thing to reverse the process. So HTC, doesn't really know how or when they will be able to unlock the bootloader on the Sensation. Here' a quote from the above support chat session,
We are currently developing new bootloader unlocked software for [the Sensation]. HTC is still committed to allowing our customers to unlock the bootloaders if they wish, however we are still implementing the policy and many updates were already finalized prior to our change in policy. We apologize for the inconvenience, but be assured that we are working on a solution for our customers and our commitment has not changed. Please stay tuned to our official channels for ongoing updates on how we will be implementing this policy.
We will inform you guys as soon as HTC figures out a solution and shares it.

Source: AndroidPolice