Please disregard my prior post, Everyone.
As far as is known, this exploit is NOT in the wild at this time. . . but now that it has been demonstrated, it is only a matter of time. The saving grace is that it requires the malicious hacker to have physical access to your computer to accomplish this hack. . . but once it is done, there is NO WAY for the user to know it was done! There is no way for the user to recover aside from having the system ROMs re-flashed. . . which is something very difficult to do. Don't let your maid have access to your computer. LOL. . . of trust your household workers very well. . . not to mention your friends!
It is possible that the NSA knows about this already. . . and could have compromised computers. However, there were already means to do this without involving Thunderbolt if one had physical access to the computer. For example, with physical access, hardware bugs could be installed in the computer, mouse, cables or keyboard that would accomplish the same things. This is just one more level more sneaky.
All of you with Macs will have to put up with this until you buy a Windows PC with Windows 10m on it later this year : )