Unless
the user requests two bootloaders that are incompatible the medium can
be created.
Ignoring bootloaders is not a good idea. If the user requested
something that is not possible the build should report an error and
stop.
Yeah, that it's hard to implement from the perspective of a single
bootloader script. So I decided not to implement it.
You could add an additional script or function named:
check_compatible_bootable_pairs (as you propose) but then you need to
maintain that fictional database each time a new bootloader gets in.
That's why I decide to avoid it using it.
What it's straight-forward to implement is one of the only-secondary
bootloaders finding themselves as a primary bootloader and outputting a
warning message. But, I'm not sure what to put there as a warning. Any
suggestion?