It could also be done with a very basic driver system, but you still have to deal with pairing and all of that other fun stuff. Even Bluetooth keyboard/mouse pairing at the BIOS level would most likely require a second Bluetooth radio and PS2 or USB keyboard/mouse emulation at that level, similar to how the old PowerPC Macs could use Bluetooth keyboards and mice to do CMD+OPT+P+R and other fun keyboard tricks.
I keep a PS2 keyboard and ball mouse attached at all times for those times I really need it.