Back in the Halo: Reach days, you could use the Halo Waypoint app on your phone or tablet to bring up ATLAS, which would show you a relatively real-time feed of the map you are currently playing on. It would also show weapon and vehicle spawn locations, and how much time there was left before a respawn.
Why do you think games don't try things like this anymore? I'm sure that it would be much more polished if someone decided to put the money into this nowadays. It really is a cool concept, and most people have a second screen or just a phone they can use for it.