Re manual & DMX control....
It would get horribly confusing from a programmer / operator point of view. Its usually sensible to keep all the programming in ONE place. Once you start programming a bit in catalyst, then a bit on the desk - it becomes a big mess.... in short - DMX OR Manual keep the programming in ONE place

With regard to the camera - the intensity is controlled by the layer - all you would have to do is fade down the layer and the 'dead' camera is gone.

Solution I use for live input at the production desk is to DA the source and send it down a loom. - VLC udp multicast IP video stream would be interesting!....