Thanks for you feedback, sorry to hear your laptop died. 
Yes, agreed , its all 3: Xen / Qubes / Coreboot, and as you said, other OS’s seemed to work fine. So I don’t know really if the fix lies in coreboot or a Xen driver issue as of yet. Its a real shame as you said because this could be a really great Qubes machine. When I get a moment to go through the long coreboot build process and reflash I will still nevertheless post here, as I think most people who have this particular issue would be looking here first.
Oh ps. Mods, This subject should be linked to the HCL