I mean, you don't really need to emulate a display. Emulating serial can work enough, depending on exactly what you're looking for. I run my hobby OS mostly on serial (both on hardware and in emulators), because it's easier; but if you're trying to run existing PC software, it's certainly the case that much of it is built to run with display adapters.

The "vast" majority of these emulators were originally written to run games, and it really shows.

My dad uses DOSBox to run an ancient text editor, and we had to figure out just how to disable some of the "game stuff" to make it work for him.

It probably would be a good idea to refactor all those emulators to be supported by libvirt - it's not like the it requires the guest be the same arch.