As someone who tried (and somewhat succeeded) in writing a 2D accelerated driver (mainly blitting) for Win9x on newer Intel GPUs, this is a very interesting project --- the 3D acceleration in particular is a great piece of work. It's always nice to see the community taking over the creation of drivers for newer (virtual) hardware after official support has abandoned it.

I don't see any mention of how it handles virtualisation between DOS boxes, which is one of the more tricky bits of writing a 9x display driver.

Glide DOS is unsupported according to the feature matrix in the readme

I’d be curious to hear more about this. Was it a GDI driver?

There is also https://github.com/kjliew/qemu-3dfx pass-through 3D acceleration for qemu https://www.youtube.com/watch?v=e34mSBxDm7s