Arca Noae, the company that bought OS/2 from IBM, is adding UEFI support:
https://www.arcanoae.com/arca-noae-progress-report-arcaos-on-uefi-only-hardware/
Going off-topic: When OS/2 was created, IBM wanted to move from the OEM-cloneable IBM PC to the PS/2 system, which had ABIOS, a reentrant protect mode BIOS. Microsoft had to do a clean-room reverse engineering of the IBM PS/2 ABIOS. For Microsoft OEMs, ABIOS was a PITA for OEMs who wanted a full clone of OS/2. IBM did not publish a Technical Manual with the source code to ABIOS, unlike BIOS. 🙂
Firmware Security 