I have the display working again, but no dGPU. Linux won't boot anymore either, it fails with "NMI Watchdog: watchdog detected hard LOCKUP on CPU #" or just bootloops.
coreboot no longer hangs in PCI (I re-enabled some devices I didn't think I needed, perhaps some are critical?) and the I2C controllers appear with the "SerialIoDevMode" UPD set appropriately.