The reason is pretty simple. There's no standard that would let us craft such an app and be sure it would work across the millions of cards, PCs and OSes today.

So the setup you have should be able to work but I'm encountering folk that want a simpler method than what the OS and control panels offer. Our office writes apps and the problem is that a custom app might be possible for a big show where there's a few 100K bucks laying around, it's a custom job so it's tailored to that rig.

Parting idea. How about a video switch box to switch it around?
Bob