Have managed to jailbreak Oasis 3 after upgrading fw to 5.16.2.1.1 (couldn't get step 15 usb connection with fw 5.15.3).
But am getting the reported rootfs errors being reported with ";log mrpi" after the MR install step.
i've combed through this thread several times and it's unclear whether ";log mrpi" rootfs errors are all user errors or a problem for some kindle models/fw -- some reporting it works, some not.
**UPDATE**
this is my first jailbreak so was reticent to proceed further... Had a problem locating the KUAL-KDK-2.0.azw2 (referenced in the coplate README) until i figured out it wasn't bundled with the KUAL (coplate) repo but the KUAL (non-coplate) repo.
Installed the KUAL-KDK document, then the KOReader application folders.. BINGO!
At least was able to launch KOReader -- now to configure it and side load some epubs.
TL;DR The rootfs errors (whose error icons and messages look like fatal errors) appear to be bogus... at least for this post jailbreak install.
Much thanks to everyone involved. Given the gymnastics involved to perform the jailbreak... it's inconceivable to me how all those involved could possibly figure out how to circumvent the firmware!!