I'm not sure if it would be fun to write or just too frustrating to be worth it. Compatibility issues can get unpleasant at times. I'd suggest porting SeaBIOS to UEFI, but as mentioned, how long is real mode going to be available on UEFI-only systems? Better to buy computers built for BIOS, if BIOS is what you want, and no, they are NOT going to all vanish from the Earth tomorrow!
I hate all this "wah wah there will be no BIOS computers ever starting tomorrow!" It was not one BIOS-based
SBC released in 2018, it was one BIOS-based
SoC which is already available in a whole range of SBCs for commercial applications and one for hobbyist. If a new SoC was released, there must be other such SoCs on the market. Knowing a little about this side of the market, I'm 100% certain they will still be available new for
at least 10 years. Devices for industrial applications especially do NOT go away when they "become obsolete".
Edit: I'm sorry, that's
two whole ranges of SBCs, System On Module and Panel PC, and it's not even one SoC, it's a range of SoCs. And that's just from the
one link which appeared in these forums previously. What else is out there?