retrocomputing

In the early days (before everyone started cloning the IBM PC) replacing IO.SYS was indeed how MS-DOS was ported to other platforms, and so I suppose in theory that could work. However:

• UEFI, unlike BIOS, separates the boot phase from the runtime phase and provides far less functionality in the runtime phase. To get functionality comparable to BIOS I expect this DOS port would need to remain in the boot phase for its entire runtime.
• Since UEFI expects calls to be made in protected mode while the BIOS API is real mode, this compatibility layer would presumably need to keep switching into protected mode each time the BIOS is called, which is amusing because that's the opposite of the typical arrangement where DPMI was used to call the real mode API from protected mode in various software.
• Because most of the commercial success of MS-DOS etc were on IBM PC clones rather than the early systems that relied on the IO.SYS abstraction layer, there's not much extant DOS software that solely targets the DOS API. Some expects to call directly into the IBM ROM BIOS, and lots bypass even that layer and talk directly to legacy hardware devices that might not exist on a pure-UEFI system without a BIOS compatibility layer, so it's not clear to me that there would be much software that would run on this hypothetical FreeDOS port to the UEFI API.

Honestly, if I were trying to do something like this I'd probably shoot for a very minimal Linux image that boots directly into something like QEMU/KVM running directly against the Linux framebuffer/KMS API, since the kernel would then presumably provide drivers for the real hardware (instead of using the more limited drivers in the UEFI firmware) and QEMU can already emulate various legacy hardware that software of the DOS era tends to expect to directly communicate with.

Of course, that's not nearly as satisfying a solution as running directly as a UEFI application! I'm just concerned that UEFI isn't really designed to provide equivalent services to IBM-style BIOS, so it would be an uphill struggle.