I find Unikernels fascinating, but I’m curious as to who is running unikernel based applications in production?
Amiga games used to be written such that they would boot the computer from floppy.
You could ignore it and access the hardware directly, if you wanted, and many games did, but you could also use the OS if you wanted to.
The default bootloader would basically just say "launch the default shell and tell it to load the startup shell script file".
z/TPF is also a unikernel so Visa when processing every transaction.
Transaction Processing Facility: A Guide for Application Programmers by R. Jason Martin is a decent book I'd recommend on the subject.