Just thinking aloud:
We might actually be lucky enough for this method not to be fixed by Amazon. The mp3 bug was a serious security vulnerability which could affect inadvertent users. This one is also a vulnerability, but it's much less dangerous IMO, because it's much harder to trick an unsuspecting user into it.
As I said before, it would be nice if Amazon realized the potential of allowing users to tamper with their devices (at own risk). We already have very useful stuff around like the launcher, or the (upcoming) localization.
If all else fails, there's still usbhid mode. I'm loosely following the thread, but admit I'm too shy currently to try it out for fear of bricking the device without being able to get it back into a working state. (i.e. if things are safe to be done via USB, and recoverable by that, I'm fine to give it a go. I'm not fine with opening the device and soldering etc...)
That said, if it's possible to read/write files (or even entire partitions) via usbhid mode, then that'd probably be the way to look for a jailbreak method which is almost impossible to "close" -- or am I missing something here?