I guess it still only works for netboot then
I want to mount NFS filesystems before Kodi starts, to circumvent using Kodi's built-in libNFS to make the connection, as it doesn't play nice with specific kernel versions on my NAS. (See answer to debian - Kodi Libreelec stuttering playback from NFS share - Stack Overflow).
But from what I gather, it will not be possible to send WOL outside of Kodi. I guess I'm building my own kernel next...
Thanks for the reply and the links though!