Now I will reply my very own query, after seemingly having gone down one rabbit-hole and are available up via 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 just isn’t possible to pursuit.
The weakest hyperlink is the wifi interface, the Broadcom bcm4360 with pci id 14e4:43a0. These playing cards should not just like the bcm44xx collection. As a matter of reality, they don’t seem to be even akin 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 resembling its bodily dimensions. Not like the equally named playing cards, nobody has revealed any open-source drivers. To the very best of my understanding the wifi is nearly fully 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 is not going to implement drivers for a tool not one of the open-source working techniques help natively.
With no scarcity of voices believing information to be totally different, the very best place to look is the precise supply codes. The PCI_DEVID_BCM4360_D11AC fixed just isn’t used wherever in FreeBSD, NetBSD fully lacks the anticipated PCI_PRODUCT_BROADCOM_BCM4360 fixed, and OpenBSD doesn’t point out the PCI_PRODUCT_BROADCOM_BCM4360 fixed when enumerating the checklist of supported gadgets.
Once 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 lifeless in 2006, and PureDarwin misplaced traction round 2015. Even when there have been energetic communities, Apple would have been contractually prohibited to open-source their wifi-drivers, successfully making wifi-support macOS particular quite accessible in Darwin¹.
Supposedly there are macbooks with different wifi chipsets. I am going to depart my very own reply unaccepted, hoping somebody will finally present a solution which really provides a full resolution to the specified use-case for anybody with a supported card.