Seems some problems with trying to deliver multiple cameras streams could be solved if cameras could just "push" their video out without requiring a request for video, and if the VMS could be configured to listen for and accept the video packets without having to make a call for them. Smart switches with port-mirroring could then be used to duplicate, or even triplicate the streams without the cameras having to do anymore work than deliver one stream at full frame rate and resolutions.
From a manufacturer's perspective, how hard would this really be. On the camera side I'd think it'd just be a firmware change, maybe an optional firmware that's offered.