The issue with PC hardware is, as it ever was, hardware vendors not following the standard. Much like Apple and OS X, they build some implementation and only fix bugs if they break Windows. So if you want to build a Linux implementation, you have to implement workarounds for all the quirks in different vendors' EFI implementations, and in the meantime you can't install on their hardware.
My current laptop has an UEFI implementation that only boots from a hardcoded path in the EFI partition. You guessed right, the path of the windows 8 bootloader.
The UEFI in my home server overwrites the UEFI boot manager list every time you save & exit the configuration tool.
If I remember correctly, the UEFI implementation of a MBP that my friend and I tried to make dual boot Ubuntu required a blessed HFS boot partition for every OS.
Yea, they don't open up all their stuff, but if you dig around you can usually find a board on most chipsets that works with coreboot. That gets my purchase. Plus they are doing good work with the radeonSI mesa driver, even if they still pack binary power firmware with it (I've read a few articles decompiling and inspecting it to know it is mostly just init command code to start the hardware).