IMO, he should not have to argue against having multiple, redundant copies of drivers, shells and utilties each accessible only in its own "OS" (UEFI, GRUB, OS). It should not be a debate. This is definitely not "defense in depth". IMO, whomever controls the first OS controls the computer because there is no need for the second and third OS in order to do work (make network connections, move files across the network, etc.).
These "hardware features", whether its [U]EFI or ME or whatever acronym, IMO is a land grab by hardware vendors over what we know as the "OS". Less computer owner control, more vendor control. The sum effect of all these "features" is that verification that something is the way that the owner wants it and has not been modified is far too complex and is ultimately under control of the vendor, not the computer owner.
I do most work on the commandline in text-mode (no graphics layer) and as such I only need one OS, with some basic utilities. When the news came that new computers would have [U]EFI, I considered whether I should just switch from the OS I am using to [U]EFI. It seemed to have all the utilities I would need to do work, along with the ability to extend with new programs.
I only need one OS to boot to a working environment. I should be able to choose that OS. I hope that Minnich and Hudson and others will consider that the user may want to choose a kernel other than Linux as a source for drivers, e.g., BSD, Plan9, others incl. future OS not yet written, etc., even if it today it has inferior driver support compared to Linux, or Intels UEFI, or whatever.
The speaker seemed a bit perplexed when someone in the audience questioned whether Linux is a "TCB". What is and what is not a "TCB" should be the computer owners decision, and not anyone elses. If the computer owner wants to cede authority for that decision to a third party, then she can make that choice. But IMO it should be a choice made by the computer owner, and not anyone else.