HTC has indirectly confirmed that the Thunderbolt, will finally be getting Android 4.0/Ice Cream Sandwich soon. According to HTC, the update is almost ready for the former flagship, and should be ready for carrier approval at the end of this month. This means that the worst case scenario is that sometime in the beginning of September the T-Bolt should get the update. Here's HTC's quote,

"We're still working on getting the updates ready. We expect to have updates issues [sic] by the end of August for all devices that have been announced."-HTC
What is important about this is that the T-Bolt is NOT on HTC's list of devices that will be excluded from getting ICS. According to all the industry intel, it will be getting ICS fairly soon.

Source: ThunderboltForums via PhoneArena