I was looking thru the source to find the graphics init routines, and I am pretty sure I found it (well - once - probably couldn't locate quickly again) - the thing is such a convoluted mess, and I am not sure how much of that is due to it being an OS and how much of it is due to his style and illness?

At any rate, I think it would be possible to hack this stuff in place (mainly mode 13h - as it's the simplest, and doesn't require much to code for). I think it also needs a way to use the parallel port - mainly for a simple parallel port sound card, if nothing else. Interestingly, if you dig into the various source code examples and such, you'll find a bit about a "HD Audio" system (which looks like a soundblaster interface, if I remember my DOS hacking days) as well as a couple of bits of code for manipulating USB devices (he already supports keyboard and mouse in legacy mode, but nothing else).

Honestly - in spite of his various racist rants and views - this code is begging to be cleaned up and expanded just a bit (it's public domain - so there's nothing he could do or say about it). Overall, it is fairly accessible - just a few other tweaks could make it perfect, IMHO.