Netbooting is used by a microscopic percentage of our total users, and zero project staff. As long as we continue to receive the occasional "it still works" post when we make major changes there's no reason for us to remove netboot support, but we're equally not looking to expand support. Sorry.
My setup is described here: RE: LibreELEC v9 RPI3 PXE
For updates, I just do this:
Download the image for my Raspi, create an update directory and move the image in the new directory:
root:/nfs/Raspi# wget http://releases.libreelec.tv/LibreELEC-RPi2.arm-9.2.7.img
root:/nfs/Raspi# mkdir -p upd/p1
root:/nfs/Raspi# mv LibreELEC-RPi2.arm-9.2.7.img upd/p1
root:/nfs/Raspi# Mount the first partition of the image:
root:/nfs/Raspi# mount $(losetup --show -r -f -P upd/LibreELEC-RPi2.arm-9.2.7.img)p1 upd/p1
mount: /nfs/Raspi/upd/p1: WARNING: device write-protected, mounted read-only.
root:/nfs/Raspi# Overwrite the SYSTEM over my old one
root:/nfs/Raspi# cp -vax upd/p1/SYSTEM 3X84XbXf.boot/SYSTEM
'upd/p1/SYSTEM' -> '3X84XbXf.boot/SYSTEM'
root:/nfs/Raspi#Overwrite the rest to the tftpboot directory:
root:/nfs/Raspi# rsync -av upd/p1/* /var/lib/tftpboot/3X84XbXf/ --exclude SYSTEM* --exclude cmdline.txt --exclude config.txt
root:/nfs/Raspi#Clean up
root@ruet-ch-ars01-lin01:/nfs/Raspi# umount upd/p1
root@ruet-ch-ars01-lin01:/nfs/Raspi# losetup|grep LibreELEC-RPi2.arm-9.2.7.img
/dev/loop2 0 0 0 1 /nfs/Raspi/upd/LibreELEC-RPi2.arm-9.2.7.img 0 512
root@ruet-ch-ars01-lin01:/nfs/Raspi# losetup -d /dev/loop2
root@ruet-ch-ars01-lin01:/nfs/Raspi# rm -fr upd
root@ruet-ch-ars01-lin01:/nfs/Raspi#Well done 
