I was at FOSDEM this year (2016) and there was a talk from the leader of LibreBoot.
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.
I've been using a Raspberry Pi 3 for the past week, and have been pleasantly surprised by the performance. It's no speed demon, to be sure, but it's good enough for all my basic tasks. I wish there were a general "open computing" branch of the Raspberry Pi Foundation that would produce a $50-$100 "pro" version with more RAM and faster bus+peripherals.
The Raspberry Pi still relies on a closed-source blob running on a CPU core whose instruction set isn't publicly documented to even boot, but I suppose at least it's possible to reverse-engineer that unlike Intel ME.
Broadcom released a considerable amount regarding the Videocore IV a couple years ago. Nobody's finished writing an RTOS for it quite yet, but the ISA is now documented.
There are more "pro" oriented boards than the Pi series. ODROID, e.g. It indeed has faster I/O and better CPU. You lose out on the scale benefits from Pi.
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.
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.