Only for the record, I don't know in Linux, but on windows (at least up to 10) it is perfectly possible to use MBR partitioned media to boot in UEFI (i.e. even if generally speaking GPT is "tied" to UEFI, GPT partitioning is not a requisite unless a greater than 4TB mass storage with 512 bytes/sector is used, 4K disks are generally not bootable for a number of operating systems, but they are rare anyway as boot media).
Viceversa, it is possible with some loaders to boot BIOS from GPT (not easy-peasy or straightforward but it can be done).
As well, the FAT is only a requisite if there is not an EFI driver for the filesystem, as an example some motherboards and RUFUS provide a NTFS driver that allows booting from NTFS volumes under UEFI.
Still, while in theory GPT and UEFI have a few advantages, there is not in practice (yet) any meaningful reason to remove support to BIOS, though lately a number of notebooks have UEFI firmware only (no CSM aka BIOS), I cannot see how removing an option/choice from a distro can be a good thing.