I just successfully flashed seanikos kernel from this posting:
https://www.mobileread.com/forums/sho...75602&langid=2
I had to extract it from the update package.
So in principle, we're set to flash backup dumps onto the K3 via USB only, simply using ATK. I'm tempted to write a libusb-based version that does the same, however, it doesn't make much sense since I cannot distribute the RAM kernel (included in ATK).
This is probably the end of serial K3 rescue.
I should probably make a proper How-To.