@p >"Proprietary"? I've never used PXE for anything besides Linux
That is a proprietary kernel, full of proprietary software, so loading it consists of loading proprietary software.

The only free versions of Linux I've heard of is GNU Linux-libre and what Debian ships (although I'm not sure that's the case anymore).

>This diskless machine is now compromised! I'll have to...I guess you just reboot it and it's fine."
Some attackers love to write rootkits into whatever storage that's available, whether that's the SPI flash chip for the BIOS or UEFI, the GPU VBIOS, or another undocumented storage medium.

>In the sense that you can say you have an address, maybe. I wouldn't say that a networking protocol "works" until it can get the packets to the internet.
I can send IPv6 packets to the internet before DHCP allocates the IPv4 address.

>This is making me question what you mean by "broken" or "working".
I mean IPv4 packets are no longer being routed to the internet, while IPv6 packets are.