This is kind of a funny rule change. I understand the basic premise - offense gets it, so the defense gets it, too - but getting past that, there are a lot of little logistical things to work out.
For instance, the offense's radio is turned off at a certain point before each play (maybe once they break huddle or once they are under center, I'm not sure). When will the defense's radio be turned off? Is it when the offense's radio is turned off? If so, then the offense has control over when the radios get turned off, and that doesn't sound like it will help the defense very much. All they have to do is go no huddle and do all their checks from the line, and the defense has to go back to hand signals. If it stays on based on the playclock, then that means that the coach is in their ear making reads for them on every play, which isn't fair to the offense.
Also, defenses generally don't huddle up these days, they just all look at the coach and get the signal, then they shout out or signal to each other to make defensive adjustments. Now if only one guy gets a radio they have to huddle up around that guy or they can shout out and signal the calls to each other, so instead of the coach signalling in the calls, the middle linebacker will be doing the signals, and there's no rule against filming the middle linebacker while he's on the field. So the radio could potentially make it easier to steal defensive signals because every team is going to have a tape of them every week.
Also, what happens if the radio gets broken? That wasn't much of a risk with the offense's radios because QBs don't get hit that much (unless you're David Carr or play for Oakland), and there's a big penalty for hitting their helmet. All defensive players are involved in major collisions throughout the game, so the chances for that radio to get broken is pretty high. If it stops working, does the offense lose the ability to use theirs? If so, then I think if I'm a defensive player with a radio, I want to break it every single game. Not having the radio is a much bigger hindrance to the offense than it is to the defense, considering offenses haven't used hand signals for years, and probably don't even have any set up to use.
Just some thoughts I had on the subject... I hope the league officials have thought all this stuff out. It just seems like an "if it ain't broke" type of situation, to me.