Yes, EFI is dependent on having a GPT partition layout on hard discs, as there needs to be a special boot partition. I have always imagined EFI as GRUB(or any OS bootloader) stored directly in firmware, as in both cases, they don't load in sectors, but a boot file. In GRUBs case, the Linux kernel, and in EFI, an EFI binary file. Technically, the EFI binary header can be attached to a Linux kernel to boot the kernel directly from EFI(eg. Vmlinuz.efi)
If you think of the current Hacker's Edge, where a BOOT.SYS is loaded, it's more similar to EFI than the new block device being introduced. EFI loads a boot file from disc, over a disc sector.
I may eventually open up a pre-boot environment, where boot code is run from ROM which can be set per machine type.
I am aiming to have Hacker's Edge follow a natural hardware evolution once it's live, as this will keep things interesting and gives players a reason to return and explore new things. So rest assured that EFI will be introduced eventually. :)
Player expansion cards like graphics don't entirely fit. At least at the moment there's no system to display said graphics, and telnet can't launch external GUI windows to provide that ability. If you think of emulators like DosBox and virtualization like VirtualBox, they only emulate existing graphics cards for the purpose of making it compatible with existing OSes. VMWare did create it's own video driver to enable features like 3D accelerated graphics. For graphics expansion type cards, it would be more of a client-side application mod. I do plan on eventually making an official client, and at that time I may consider allowing it to be easily modded to add additional client side capabilities, like graphics cards. Custom hardware will really add lots of complexity, and players needing to actually write driver software to control said hardware.
EFI is still supports legacy BIOS in most machines still. If you enter the OEMs boot screen on EFI systems, you can still boot using legacy BIOS. BIOS booting is still widely available on EFI machines. GPT is also not a requirement when booting either USB or DVDs, all these devices need is a /efi/BOOT directory with a compatible EFI binary file to boot. EFI technically doesn't require GPT, but EFI is fully aware of GPT. If you download a Linux distribution ISO or bootable USB image, you won't see GPT, but an EFI boot structure on either ISO9660 or MBR scheme. These images will also most likely come with the legacy boot methods of El Torito or MBR boot sector for compatibility with all systems. I don't believe that legacy BIOS can boot GPT partitions, as legacy BIOS needs a boot sector. However, BIOS isn't dependant on any partitioning scheme, it's the responsibility of the boot sector code. The MBR boot code checks the MBR partition table for the active partition, loads the first sector of said partition and executes it.
Technically once block devices are rolled out, you can emulate what EFI does without a firmware. Create a new small block device which you can call ROM. Have this as the first block device as read-only. The second block device would have a GPT partition table and no boot sector. Your EFI ROM block device will load first and check the partition table on your GPT block device, and allow you to select which .efi file to boot on that disc. This has actually been done to allow non-EFI machines to boot EFI. It's widely used in the Hackintosh community as OS X requires EFI to boot. The EFI boot code for BIOS-based systems is called XPC EFI Bootloader, which uses EFI developer tool called DUET to boot EFI from MBR boot code.