We are definitely willing to add NetBSD if someone can demonstrate it working well with iPXE. It's come up several times and it's implementation works with pxelinux in a local setting but not so well with iPXE as the implementation linked looks for a specific file on a tftp source.
Most of my testing was just allocating an ARM machine on Equinix Metal as I didn't have much ARM hardware to test or qualify on. I've also gotten the bootloader and menu to work with an RPI4 but loading operating systems on one was a bit more challenging given reduced memory on the hardware.
There is ARM support as well in addition to i686/x86-64. Operating system versions are typically dropped as they go EOL upstream from the menu, we try and keep the menus up to date as changes and new versions are released.
Sounds like Spotify is trying to make is as hard as possible for the coming exodus to Apple One as there is more perceived value in the Apple bundles than just paying for a single Spotify music subscription.