So when I initially read this thread, I thought that there might be some GPL violations going on with this. And now after coming across this article today it sounds like this is almost certainly a GPL violation (as would be Proxmox with ZFS included)
Interpreting, enforcing and changing the GNU GPL, as applied to combining Linux and ZFS — Free Software Foundation — working together for free software
Interpreting, enforcing and changing the GNU GPL, as applied to combining Linux and ZFS — Free Software Foundation — working together for free software