It's only dramatic change if the purpose of the system is to identify as many people as possible (i.e., data mining the crowd), rather than to scan for a fixed

It's only dramatic change if the purpose of the system is to identify as many people as possible (i.e., data mining the crowd), rather than to scan for a fixed set of known individuals (which is what guards already do). It's like the difference between checking IDs for entry vs scanning and saving IDs for entry.