A dedicated camera button on, say, the next iPhone, would be amazing. Not just one to that opens the camera app or works as the shutter when it's open, I'm thinking one where you could single press to take a photo, and hold to start taking a video, whatever state the phone is in.
The ubiquity of camera phones has been a revolution in recent times for covering police brutality, civil rights abuses, and tragedies like yesterday's explosion in Beirut, but often things happen so quickly that videos are of the aftermath more so than of the event itself. Capturing things even a few seconds sooner could make a huge difference, and I struggle to think of a software shortcut that could work as quickly.