I don't remember whether the video BIOS was extracted from the old binary or if it is the open-source replacement, but I'd tend towards the latter as I don't remember searching for the backup/dump of the original firmware.
And yes, it's running coreboot, and at least CLI/linux-framebuffer arch linux works. I didn't yet get to setting the rest of the system up, but considering I bought it specifically for high-security operation, as the ME can be physically removed without loosing more than the build-in Ethernet port, I'm not pressed to do it anytime soon.
Edit: I'm pretty sure I followed [0], which leads me to the new conclusion that I did use libreboot, a more strict version of coreboot (think coreboot=Archlinux, libreboot=GNU Guix), and had to fiddle with the question whether the open-source video bios would work. This confuses me a little, as I remembered buying an X61s, not an X60s, but from the fact that it booted after flashing, I deduce it had to be an X60.
[0]: https://libreboot.org/docs/hardware/#list-of-supported-think...
