So, I was able to get a more detailed description on what seems wrong with my images, but I have no clues on how to fix it.
I found that I cound use "-serial stdio" parameter to qemu to get the full boot output on the console, and I appended the "console=ttyS0" parameter to the boot screen on the qemu window.
The output seems to be related to errors mounting the root live file system, hence it does not seems to be able to run the expected /sbin/init from systemd.
These images were built using the live-build package from jessie (4.0.3-1).
Any clues on what I did wrong?
Best regards,