The money quote from the linked coreboot blog post is:
Laptops with libre operating systems have existed for
decades. The only real innovators in this area have been
Google and GluGlug. Google ships partially free
firmware, although insufficiently libre to be able to
provide the “respect your privacy” guarantee. GluGlug
can make this claim, and it ships laptops with fully
libre firmware. The downside of GluGlug is that it’s an
aftermarket add-on. GluGlug and Google have been in
business far longer than Purism. So, what has Purism
brought in that’s new and exciting and libre? Nothing.
The content of the post is disputed in the comments by someone who claims to be a "volunteer of Purism project":
Purism is actively working on porting coreboot to Librem15 with
some coreboot developer(s). @mrnuke is more than welcome to join
the effort :) There, that's the truth about Purism.
Purism’s Librem 15 will ship with an Intel CPU fused to **run unsigned BIOS** code
This is apparently the first time a laptop is (almost) available with a recent Intel cpu where this is the case. This is needed for an attempt to port coreboot to be possible.
That claim only deals with Haswell since before that, there was no fuse to prevent running unsigned BIOS code (also known as Intel Boot Guard).
Since there are Haswell Chromebooks, there are devices on the market that also provide this feature.
The limitation for libreboot devices using recent Intel chips is the ME firmware which is always signed, but not on the CPU and not BIOS code. So the statement is technically correct - through some _very_ careful choice of words.
