I am the creator of ~40% of the 10.12/13 patches including the USB driver.
dosdude1 and I have been investigating GPU drivers for most of the day and sadly we think it is not possible for any non metal GPU to work, because almost the entire OS uses Metal.
Evidence: Remove metal driver, it won't boot. Remove opengl driver, it boots STILL WITH ACCELERATION but stuff crashes. Also, removing the opengl software renderer doesn't break safe mode, so it must have a metal software renderer.
This leaves the compatibility list as theoretically
Xserve 2008 with new gpu
Xserve 2009 with new GPU
Mac Pro 2009
Mac Pro 2010/2012
Oh that's sad. Well, thank you very much for taking the time to test all that so thoroughly. Just as a curiosity, it should boot with
every gpu driver gone EXCEPT the framebuffer kext:
HD original: AppleIntelHDGraphicsFB.kext
HD 3000: AppleIntelSNBGraphicsFB.kext
HD 4000: AppleIntelFramebufferCapri.kext
HD 4600/5000: AppleIntelFramebufferAzul.kext
HD 6000: AppleIntelBDWGraphicsFramebuffer.kext
HD 5xx (Skylake): AppleIntelSKLGraphicsFramebuffer.kext
HD 6xx (Kaby Lake): AppleIntelKBLGraphicsFramebuffer.kext
INTEL driver note: EACH generation has ITS OWN framebuffer kext. I.e AppleIntelKBLGraphicsFramebuffer.kext for HD 6xx and an ARCHITECTURE-SPECIFIC accelerator kext (i.e AppleIntelHD4000Graphics.kext for Haswell, which loads AppleIntelHD4000GraphicsGLDriver)
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Nvidia (ALL CARDS, stock drivers): NVDAResman.kext
Nvidia (ALL CARDS, WEB drivers): NVDAResmanWeb.kext
Note that stock drivers support: 8xxx, 9xxx, 2xx, 3xx, 1xx, 6xx, 7xx (tesla, tesla, tesla, tesla, tesla, kepler, kepler)
WEB drivers support: all stock, plus 4xx, 5xx, 750, 9xx, 10xx (fermi, fermi, maxwell rev. 1, maxwell rev. 2, pascal)
WEB drivers support all the architectures since tesla. So, if a quadro/tesla gpu has one of those architectures, then it will work, as well as some exotic laptop cards if NOT optimus (8xx mobile).
NVIDIA driver note: All cards use a SHARED NVDAResman (framebuffer kext), and an ARCHITECTURE-SPECIFIC accelerator kext (i.e NVDANV50Hal.kext=Tesla) that works with any cards matching it.
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AMD:
HD 2xxx: AMD2400Controller.kext, AMD2600Controller.kext
HD 3xxx: AMD3800Controller.kext
HD 4xxx: AMD4600Controller.kext, AMD4800Controller.kext
HD 5xxx: AMD5000Controller.kext
HD 6xxx: AMD6000Controller.kext
HD 7xxx: AMD7000Controller.kext
AMD8000Controller.kext and on: TODO
AMD driver note: EACH card ARCHITECTURE (Evergreen=5xxx, Northern Islands=6xxx, etc) has ITS OWN framebuffer kext. I.e. AMD5000Controller.kext for AMD 5xx. NOTE: This rule doesn't match for the earlier cards. One was typically for the low end series, while the other was for the high end series. However, those cards are so ancient they probably won't be used by anyone on this thread and certainly no default gpu.
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Therefore, it is very odd that taking out the MTLDriver stops the GUI start. In previous versions, you could even boot without any kexts loaded (like for a 7300GT, it would still show 1024x768 without any framebuffer at all on an unsupported macOS like 10.11) but now taking out the actual accelerator driver crashes the GUI. Maybe we could test with JUST the framebuffer kext loaded to get correct resolution and nothing else? That's how it used to be, and in safe mode what would happen is the only kext loaded would be the framebuffer kext (to get correct resolution on real macs.) I wonder what safe mode does now, now that the MTLDriver is REQUIRED for the GUI. Perhaps they'll fix it by the public release timeframe, as by then people will need to be able to safe boot with the GUI working. Safe boot is done by holding shift during boot.