According to OP this does not disable bootloader unlocking in itself. It makes the up-versioned devices incompatible with all previous custom ROMs, but it should be possible to develop new ROM releases that are fully compatible with current eFuse states and don't blow the eFuse themselves.
I understand that there is a nuance somewhere, but that's about it.
Can you explain it in simpler terms such that an idiot like me can understand? Like what would an alternative OS have to do to be compatible with the "current eFuse states"?