I had a discussion similar to this with RMS a while back and he seemed to think that the x86 and ARM architectures were completely hopeless for this because of the management engines etc. At that time there were credible attempts to build completely blob-free POWER9 systems, so Ifigured that was the thing to get once they got a bit more affordable. I don't think the Talos stuff ended up blob free, but it is way less blobby than x86 stuff. Maybe there is hope of blobless RISC-V systems some day.
The Talos II is blob-free. At launch, proprietary binary-only firmware was required for the network interface, but Raptor Computing Systems offered a bounty to reverse engineer and do a Free Software re-implementation of the firmware, and that effort succeeded and the bounty was paid. See:
Most processors with Arm cores do not have "management engines", in fact lots are almost blob-free. Some like Marvell Armada 7k/8k can run without any blobs.
