Sure, but it also doesn't make it necessary or useful to implement booting from that port - booting from a port IMHO is not a feature that Apple wants to offer

Sure, but it also doesn't make it necessary or useful to implement booting from that port - booting from a port IMHO is not a feature that Apple wants to offer to its target audience at all, so it's sufficient if some repair technician can do that according to a manual which says which port to use in which scenario.