Ok, the EFI ROM need not be on the gfx card. But we have no idea what the next Mac Pro will be. We don't even know if it will take PCIe cards. But if it does, these cards will need an UEFI ROM to show a boot screen.
The EFI needs to know about the port layout of a card to show anything on screen. You can't have a generic EFI firmware on the motherboard that just works with any graphics card you put in a Mac or PC.
Consider also that the card ROM control many things beyond the boot screen, so it needs to be on the card itself anyway.
And this had nothing to do with Sierra. The 2006 Mac Pro had the Radeon X1900XT PC BIOS on the motherboard ROM (which was added by the Bootcamp-enabling firmware update). This allowed the card to boot Windows without it having a BIOS (it was perhaps the only pure-EFI Mac card).
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Ok ok we know that. But we're in the Mac Pro forum. It was with Sierra on the cMP we first noticed the screen could initialise and load like Windows on a PC. Hence my post is basic. I didn't want to waste time to write an essay with all the details because this is just a forum and not some place I use to exploit people with overpriced modified graphic cards. I have no need to waste time trying to look like the local don.
You could just have admitted you were wrong without resorting to that.
You said that Sierra was the first OS X that could initialise a video card wihtout the need of the EFI ROM "on the GPU". For one, a BIOS cannot be on a GPU, it has to be on a separate chip. And if the GPU cannot be changed, the firmware may well be on the motherboard's ROM. That has nothing to do with Sierra, as Netkas said. Any non-tower Mac have had this for years (even the 2006 Mac Pro X1900XT has, as I said).
The tube Mac Pro video boards cannot be changed by the user, so their firmware can also safely be on the motherboard ROM (though I'm not sure if it's the case). It doesn't tell you anything about the 2018 Mac Pro, since its GPUs may well be upgradable.
Anyway, having a GPU firmware on the motherboard ROM chip doesn't make a Mac "more like a PC". PC video cards need to carry their UEFI/BIOS, just like Mac Edition cards.
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The drivers are loading a little earlier now so we can see the end of the boot process, nothing else has changed. There's no EFI stuff involved, just the system drivers kicking in. You won't get the boot manager, FileVault or any other pre-OS EFI video like that.
I think this new behaviour where the video drivers start before the progress bar finishes was introduced together with the progress bar itself. It was new to Yosemite or El Cap, but not Sierra.