[fsflover]

Coreboot with Heads exists and works fine for me with Qubes OS. So it's not a hypothetical.

[hollerith]

Coreboot with Heads and Qubes prevents malware that has inserted itself into the firmware of your ethernet driver, keyboard or block-storage device from modifying your software?

[fsflover]

Yes? Qubes provides compartmentalization for the hardware you listed.