I doubt Harley will make a fairing for older bikes, I'm assuming your want the double din stereo....and weather the new fairing will fit older bikes is a toss up...I understand the 2014 seats will not fit 2013 and older bikes....
I'd say that if you are good with parts manuals, you might be able to cobble together a way to get the new fairing on the older bikes. The electronics in the new fairing would be a different issue. You would need new hand controls, new inner and out fairings, all the little parts that go with it from the parts diagrams. If I had to guess, it would likely be way more expensive than taking the hit on a trade in. We won't know for sure until they release the 2014 parts guide and someone takes the time to make a parts list and price out the upgrades. I can't remember if the 2013 bikes had a body control module or not. If not, it will likely be REALLY expensive to update the electronics. This is all speculation at this point!