I hope that such a feature will eventually be in the game, but it seems like something that would just be frustrating to have on public servers.
For a standing start, there would have to be sensors to detect that each car is in position. How far outside the box would a car be allowed before it got a penalty? On a full server, there would inevitably be someone who gets a kick out of driving too slowly on the pace lap and stringing out the field, or crashing into cars on the warmup lap. There would have to be some way of determining that a car is out of position, and it would have to be able to detect a car accidentally passing another car for a second or so. One guy is warming his rear tires, another is warming his brakes (brake heat modeling will be in this sim eventually), they meet in the middle or pass temporarily. Innocent drivers shouldn't be accidentally penalized because of some idiot, or for making a small mistake. And for rolling starts, how bunched would the field have to be? How could the game detect proper spacing? What would happen if the field isn't close enough?
It seems like if such a system were to be implemented on public servers, we'd spend all day in a futile effort to get everyone around the lap without making stupid mistakes and actually see the lights. During league races though, absolutely. But those guys can be counted on to drive properly behind the SC without such silly auto-detection functions already.
For full-course cautions (aka safety car periods in F1), how would the game determine that the caution is serious enough to warrant bringing out the SC? There really needs to be a human element to make the judgment call, and to require a real person to oversee every single race is just impractical.