Use your favourite bootloader as a payload, so the Windows installer can't overwriting it anymore.
Load emulation for IBM PC BIOS, OpenFirmware, EFI, etc. when needed.
Protection against (some) rootkits built into the "BIOS" payload.
System check utilities (e.g. memtest86) integrated into the "BIOS". (I can also imagine some special tools to pop up for overclockers & such to test/optimise their system.)
Rescue system in the "BIOS".
Integrate simple games into the "BIOS". (Imagine CoreBoot Solitaire booting in 1 second, that would be a killer app! )
Coreboot might be interesting for the enthusiast or code hacker. Coreboot is literally nothing to an end user. To dive into the car analogies, BIOS is the oil filter. Most of your population doesn't care what brand or type is down there as long as they can go placed.