A better video (not my video)
Confirmed by MVC on Netkas http://forum.netkas.org/index.php/topic,13881.0.html
Confirmed by CreatePro on MacProUpgrade on FaceBook
EFI UGA has also been located in RTX 2080 roms!
Very interesting. So while people here were arguing why this couldn't be possible, I downloaded a random RTX ROM from TechPowerUp (Asus.RTX2080.8192.180831.rom) and had a brief look at it. Besides its enormous size (1MB, seems to contain to identical copies of the same VBIOS and UEFI) I found an interesting bit in the decompressed UEFI binary:
Offset 1A28: 8B29 2C98 FAF4 CB41 B838 77AA 688F B839
That's the definition of EFI_UGA_DRAW_PROTOCOL, sitting right next to the definition of EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID (Offset 1A18)!
My experience with other UEFI ROMs is quite limited, but a quick look into an GM204 UEFI binary revealed just the GOP part, but no mention of UGA support (and as we all know, they won't output anything in a cMP unless flashed).
So this might actually be legit!
I don't think that's an issue. 4K boot screens have been troublesome, because the original "Mac Edition" EFIs didn't support DisplayPort 1.2. My Dell U2515H in DP1.2 mode won't show anything either, although it's just WQHD. On the other hand, 4K boot screens do work on HD 7xxx or Kepler GPUs when connected by HDMI 1.4 or DP 1.1 (obviously not 60Hz in this case).
The RTX UEFI drivers will surely support DP 1.2.