Unfortunately, today most graphics hardware relies on drivers for specific versions of specific operating systems.

Mmm? Earlier and every console system generation have a BIOS even a Atari 2600 have it.

Unless I am misunderstanding your comment?

MS-DOS is about files -- and AFAIK most games did not re-implement that part, nor they re-implement BIOS drive handling which was sometimes machine-specific. I certainly remember playing games from Novell Netware shared drive, which would be impossible if they re-implemented filesystem support.

And none of the games I know was taking over the boot process as unikernels do. It was always: start DOS, configure system with MSDOS's CONFIG.SYS / AUTOEXEC.BAT, and only then start the game. Not very unikernel-y at all.

Now BIOS video services were very common. BIOS "int 10" was great at setting video mode, but it sucked for everything else -- even in the text mode, we often read/wrote to framebuffer directly.

Not sure about keyboard -- the hardware is fairly simple, so it would be easy to reprogram... but also BIOS did a satisfactory job handling it, so it was OK as long as you keep interrupts enabled.

And as for mouse and sound card, those did not have any DOS drivers to begin with.