And even if I installed the jailbreak, it could still limit me to uselessness. Not sure if KUAL would work in this mode, and installing MKK would be a huge PITA with no UTK menu.
I wish I could get that UYK bootmode to work, but the documentation is confusing, mentioning USB OTG mode. Perhaps it tries to load a firmware image from a USB stick an an OTG cable? What is confusing is that some i.MX6 dev boards use imx_usbloader when a similar button is pressed on their dev kits. There are TWO bootmode pins on the SoC, so perhaps this button tirggers a behavior different from the magic key on earlier kindles -- like loading firmware from a flash drive on OTG, perhaps.
I really wish this had diags with usbnet...

Time to hunt for a USB serial adapter.