Bonus points if you can overlay artwork over the ntsc monitor. Ideally monitors would be devices and you could plug different ones in.
Yeah, they probably deserve to be emulated properly with their specific technical limitations, knobs, buttons and their occasional status LCD displays. Having 3D models with a display texture would be more with the times than image overlays, though. ;P
There's a whole untamed world of monitor diversity out there. I even knew of somebody with a monitor that displayed certain small resolutions really
tiny instead of stretching them out to fill the screen. Not that this would ever become a priority or anything since HLSL can simulate the "standard" stuff, of course.
Regarding which monitor would be compatible with which device, I don't know how MAME does this kind of things, but I guess it could be handled by having a list of connector types and just allowing those that physically fit? Although this could be done with anything other than monitors, including game cartridges...