z4root will most likely never be able to root any new HTC device. Let me rephrase that, it will most likely never enable permanent root on an HTC device. I think I remember seeing that it can root HTC devices but once you reboot the device becomes un-rooted again. The reason behind this is because you need to turn S-off in order to obtain permanent root.
If z4root could temporarily root the Thunderbolt, I don't think it is capable of doing so as of right now either.