It seems that someone may have managed to jailbreak iOS 7 already. It’s not totally clear if they have, but by the looks of it, Ryan Petrich, a developer may have accomplished it. However, it doesn’t’ tell us much.
The screen basically shows an iPod touch with his Cydia Tweak, Activator, running. However, it says “System version too new.” It also mentions that the tweak “has not been tested on this version of iOS.”
Also, there are dock icons that are definitely iOS 7. Perhaps developers have figured something out, and are planning to release a jailbreak soon after the release.