This is a good reason why it won't, there will always be those that will try and enjoy the challenge and experimenting.
http://forums.macrumors.com/showthread.php?p=15295924#post15295924
UEFI was not finalized and adopted, the firmware in the Early 2008 Mac Pro, until late 2007, and that machine needed EFI and SMC firmware updates, and those machines also - lately - seem "finiky' even now with sleep, power on, and other things - threads don't ask users if they had the very early, first month or two vs later post-EFI/SMC done at the factory and with new ROM chips.
UEFI (EFI64) is what Intel and Microsoft along with Apple adopted for 64-bit operating systems post Vista SP1 (not sure, Apple did not have a separate path and it has only been 10.6.x that booting a full native 64-bit mode existed. Meaning that the MacPro 3,1 and before were never really proven and tested either.
"We" as a community may not mind buying ATI 5770 to use Lion and beyond but who knows what the rest are doing, having shelled out $279 for Nvidia GTX 8800GT once perhaps already (and maybe seeing that die), or $399 for ATI X199.
2009 was the first time that testing of Snow Leopard and 64-bit mode was really possible.
Take the support for 3TB drives and really pushing to see just how well EFI and GUID support was which was "introduced" and improved (changed and modified) but began in 10.4.6 even though it was mentioned before then.
The Mac Pro 1.1 EFI32 existed in limbo with Intel Skulltrail reference motherboard back in mid-2005 so it was already more than a year old, and is 7 yr old design.