Shuttleworth: ACPI, firmware and your security

Describe what you need to get to the next step: load two files in memory and run Linux.
For that, you need to know how many hard disk there is and few information on how to read them, you need to be able to display stuff in case of error, and you may need access to the keyboard/mouse if there are different solutions the user may choose.
I agree those interfaces have evolved over time in the BIOS since 1983, but backward compatibility was a major concern; you can have full graphic display and mouse support, CD/DVD reads, USB disks and mouse/keyboard on current PC (with basically the same interface).
What you really do not want to do is to have a real operating system at this level, querying the PCI, DMI and ACPI to detect how to read two files and display a possible error message, before running Linux which will redo the same querying in its own way.
A PC already probe once keyboard, screen and disks at boot (to display the BIOS setup and load the first sector of a disk), Linux will probe itself anyway all the information needed to run mutiprocessor with highly optimsed drivers, there is no need to probe in the bootloader.