On their FAQ page: https://libreboot.org/faq , you can see the question "Why is the latest{Intel,AMD} hw unsupported?"
They go into more detail than the provided link. Also, dropped supports starts in 2008 for Intel, 2013 for amd.
The truth is: we need something like this to protect the whole boot process. But unless we can put our keys/sw in there, we will never be sure.
Honestly, his talk on the state of the project was very bitter. He literally said that there is absolutely no hope that LibreBoot will ever be able to cope with ME, and that the fight is over since 2008.
As much as I would absolutely love to be able to run a free firmware, unless there is a major change/outsider in the hardware manufacturer world, it seems very unlikely that it will be possible on current x86 architectures.
https://www.broadcom.com/docs/support/videocore/VideoCoreIV-...
Few if any of them have "enterprise" grade quality IMO. The ones that strive for this (HP Moonshot, e.g.) are significantly more expensive than $50-100.
Note that the topic at hand is binary blobs and trust and Pi and other ARM SoC fall short there.