Now I can reply my very own query, after seemingly having gone down one rabbit-hole and are available up by one other.
Because the dialog within the feedback on the query goes, it ought to most likely be doable to put iPXE in an Apple Disk Picture inside a NetBoot Picture and chainload into it utilizing BSDP. Nevertheless, as at all times, the satan is within the particulars and with my particular {hardware} (MacBookPro11,1; A1502 EMC 2678) this concept isn’t possible to pursuit.
The weakest hyperlink is the wifi interface, the Broadcom bcm4360 with pci id 14e4:43a0. These playing cards aren’t just like the bcm44xx sequence. As a matter of reality, they aren’t even corresponding to different bcm43xx playing cards. The one datasheet one can ever discover for them, not less than with out signing an NDA, is a skinny eight web page doc describing trivial issues equivalent to its bodily dimensions. Not like the equally named playing cards, nobody has revealed any open-source drivers. To one of the best of my understanding the wifi is nearly utterly unusable with FreeBSD, illumos, NetBSD and OpenBSD. They solely work underneath Linux if loading binary blobs offered by Broadcom (alpine, arch, debian, ubuntu). One can safely assume that iPXE won’t implement drivers for a tool not one of the open-source working methods assist natively.
With no scarcity of voices believing details to be completely different, one of the best place to look is the precise supply codes. The PCI_DEVID_BCM4360_D11AC fixed isn’t used wherever in FreeBSD, NetBSD utterly lacks the anticipated PCI_PRODUCT_BROADCOM_BCM4360 fixed, and OpenBSD doesn’t point out the PCI_PRODUCT_BROADCOM_BCM4360 fixed when enumerating the record of supported gadgets.
After I was given this pc a fews days again, I believed one might run an open-source Darwin on it. It appears nonetheless that OpenDarwin was introduced useless in 2006, and PureDarwin misplaced traction round 2015. Even when there have been lively communities, Apple would have been contractually prohibited to open-source their wifi-drivers, successfully making wifi-support macOS particular reasonably obtainable in Darwin¹.
Supposedly there are macbooks with different wifi chipsets. I will depart my very own reply unaccepted, hoping somebody will ultimately present a solution which truly provides a full resolution to the specified use-case for anybody with a supported card.