DriverKit
developer.apple.com
developer.apple.com
For me at least, the process of putting together a hackintosh isn't very hard at all.
First I research hardware that is compatible that I can source at a good price. This is the key step since non-compatible hardware is a world of misery. I'd say in the order of 50% of motherboards and 75% of graphic cards have this attribute. This is the hardest step and the community could make life easier for everyone if it maintained a database of such parts but sadly it's mostly geared toward people getting the hardware they already have to work.
Second I get a flash drive of some variety, format it and run the Clover installer on it, then I drag the EFI folder from the standard archive from olarila.com onto the EFI partition of this boot drive. The Hackintosh is now bootable as a vanilla Mac. The boot drive remains attached at all times to enable this.
Finally I install macOS as it was a real Mac, from an installer flash drive, booting through the Clover boot loader on the boot drive of course.
The reason I use macOS (and always have, previously on Apple hardware) is because it delivers a superior user experience. The OS software is far and away more usable than Windows and Linux machines. There is no sign either of them are catching up.
That said, I've switched to an eGPU setup with a Radeon Rx580 and my 15" mbp, and it largely gets me to where I wanted to be with my hackintosh. Using an eGPU with macos is surprisingly easy.
The software has improved a lot recently. Plugins like WhateverGreen and VirtualSMC means there is broader hardware support out of the box without fiddling with settings.
But yeah if you are happy with Mac hardware then Hackintoshes are entirely pointless. Laptop Hackintoshes are also more challenging without really competing with comparable Mac hardware.
But I really don't understand why people make their OS drive their boot drive. Besides the potential for catastrophe it also means you can't move the OS drive between machines or do OS drive backups freely.
There's also always the ability to recompile the Darwin kernel, as AMD Hackintosh users do. This does have the downside of making updates annoying.
https://twitter.com/felix_schwarz/status/1135672295941427200
nVidia coasted on having been used in some of the mac hardware thus having access to at least some versions of the APIs, but it seems that what they have no longer works with Mojave.
Pretty tiny domains, though.
Honestly, those are the only professional use-cases for multiple GPUs I'm aware of. CAD uses GPUs, but not multiple and I don't see AMD having any lead over Nvidia. Same with other uses like GPU acceleration in things like Photoshop or video editing--1 decently fast consumer grade GPU is enough. I don't see farms and 4+ cards per box.
Adobe Media Encoder (and by extension Premiere and AE) can do multi-GPU rendering as well, which starts to matter when you have huge comps. I've worked with 2D animators who need to turn around footage really quickly and a bunch of them are on multi-GPU rigs.
Adobe Media Encoder does seem to support OpenCL and CUDA, but the GPU acceleration only looks like it works with certain transforms and filters, not with encoding. So I can see it helping 2d animators, but much less so for video editors--especially with multiple GPUs.
I feel like GPU rendering has been teased for like 10+ years now. Only within the past few years am I seeing studios upgrade their render farm in earnest to accommodate GPUs.