Flying fighter planes is a dangerous occupation. Not all accidents can be prevented. In this particular case I doubt a system like what you suggest would have helped, and even IF the F/A-18 had such a system, it probably would have been disabled to allow the planes to perform the demo. Those are specially modified planes, with highly trained pilots. They don't wear G suits either, were every other pilot of that plane is REQUIRED to wear them. Why? Because when the suits inflate it can bump the stick. Not something you want happening when your flying 18 inches from anouther plane.
It sucks that this accident happened but at low alltitude and high speed, when something goes wrong, even the fastest computer on the planet probably wont save you. Those guys understand and accept the risks involved with their job.