Looks like our wait for ICS is almost over. According to several sites there is now an official leak. There's a ROM out based on it that has been slightly modified by Team BAMF, but it may just be pending VZW approval before a push.

HTC ThunderBolt Ice Cream Sandwich build leaks | Android Community
HTC ThunderBolt Ice Cream Sandwich Update Leaks

Yes, they're talking about a root-required ROM, but that ROM is apparently based off an actual TB build that is pending approval.