Not even when you can't see the ball though. How many times do we see an angle and they claim that they can't say exactly where the ball was because they don't have a straight shot across the field when it's happening. Goal line would obviously also be huge. There are a lot of times when you have no idea where the ball is at but you can see the runners legs. It happens way more than 3-4 times a season.
We as big fans, fanatics even, remember it happening in many games, but is it really happening that many times in a season?
Sure, if the system's already in place then yeah go do it. But it's not. It's a totally different implementation to stream all that data live against a synced game clock (to the fractional second). Hell just regional latency is going to cost you anywhere from 25 milliseconds to upwards of two seconds.
Right now, they probably manually download random chip data from select footballs with a reader post game. I seriously doubt they are wirelessly transmitting their location to a live receiver which is a totally different setup.
Imagine seeing the knee down and the chip data is off by a half second so it shows you a spot two yards back. You'd need a local server and data capture at each gamesite to start with, and the software engineering costs would be significant.
Companies have to make decisions like this all the time when it comes to real time data processing vs batch offline processing, and you save the real time for the most critical situations (like wire transfer fraud detection). Implementing it for the NFL would almost require there be a lot of applications that could benefit from the platform.
Exact ball placement that I could really trust to be synced with game film just for those few cases where I can't see the football but I can definitively see the player's knee or foot out of bounds, etc-- lot of bucks, almost zero bang.
But purely as a fan of the game, if they got it right-- cool.