Yes I did.
I was still stuck in the "writing system" test, and rebooted the device. As I feared, the system didn't boot, so retried the stock kitkat flash through NRT. The second pass got me to the same result, stuck in "writing system" with the device saying "fastboot okay".
I decided to reboot to recovery, and wiped both system and cache partition. When I reboot, I was able to see the kitkat startup screen, and then everything went fine.
Eventually, I'm not able to tell what went wrong or good with the flashing, but here are my observations and facts :
- once launched, the system initialized correctly, and I didn't encounter any problem since then
- even if the system partition appears to be flashed correctly, I was still amazed that everything works, since the user partition hasn't been written
- only the stock system has been installed. No root nor custom recovery.
As for the root cause of the initial OTA problem, I think it was caused by lack of battery power.