I dual boot with Windows 8 for games. Windows 8 will work without UEFI, but I haven't found any information about how to downgrade an existing UEFI-based windows 8 partition to legacy bios, or if it is safe/feasible to do so. In particular, the non-existent bootloader. (Windows, as usual, seems to take the approach of "wipe + reformat", which is not exactly optimal.) If you have any ideas, feel free to let me know.
Not addressing any other of your points, doesn't most laptops/computers which ships with UEFI allow you to set it to boot in "legacy-BIOS" mode?
Even if you're currently UEFI-booting, I would be seriously surprised if UEFI-support was a requirement for every OS your machine can boot.