** On another point, is it possible to JUST move /storage to a USB drive and just leave a symbolic link on the SD card? Most of the configuration and I/O on a working system is to that mount point, so you would have the system on the SD card and the user data on a USB drive.
this is exactly what is happening if you copy or move /storage to a harddrive and change cmdline.txt to: (as gark81 also writes, or use uuid as you write)
boot=/dev/mmcblk0p1 disk=LABEL="labelofyourhardrive" quiet
system will be on sd and userdata on harddrive.
if the symlink thing will work i have no idea, i never seen it done that way but i think you could run into trouble.
the problem with moving the system image from sd card and change boot in cmdline.txt is when you update. the firmware/bootfiles needs to reside on sd and will not be updated. i guess you could update these files manually, but there really is no reason to move boot.
at least thats how it was on openelec, i suspect it is the same on libreelec.