If we can get the FXZ I have an idea of how locked users can keep root, but, they must never take the OTA. Once they do, I can't help them anymore. The idea I have is what they did on the S4, and I hope to get some help with it. Basically it's this:
o) Make sure you're rooted, stock 9.30.1
o) Install SafeStrap
o) Boot into SafeStrap, flash a script that updates the system partition with the stuff from KK, keeping root in the process
o) Immediately boot into AP Fastboot
o) Run an RSD script that flashes all partitions EXCEPT: system, GPT, and TZ and obviously keep data
That's the theory. But we need the FXZ to test whether you can flash certain partitions from KK, then flash back to 9.30.1 using my UNIVERSAL script for both. If that works, then we should be able to pull this off.