They are going to use coreboot, which is free but includes some binary blobs from Intel. I don't think you can boot any modern x86 without a binary blob from the CPU manufacturer, unfortunately.
I also don't think it's possible to get any modern machine up without some device firmware blobs. The best-case is that all the blobs are provided onboard so the OS doesn't need to provide them, but they're still there and we have to trust them.
Purism seems to me an incremental improvement and I might buy one, but I really hope for a truly free machine someday.