I think an auto-film idea has been brought up in the past, and I still think it is a good idea. I am not so sure about a pure "gun-cam" as it sounds like you want. A lot can go into a fight before you actually pull the trigger, and it is the lead-up to guns-solution where you can see what you did right or wrong.
I can't remember who was the first to ask this, but the best idea IMO would work something like this. A player would have the option to auto-record his sorties in his flight preferences. If selected, the film would roll automatically every time he launched. At the end of each sortie, when he returned to tower (shot down or landed), there would be a pop-up that would ask if you wanted to save the film, and ask you to name it. If you decided nothing worth keeping happened that sortie, you could just click "no" and the film would be overwritten by the next sortie. If you did save it, giving it a name would make it easier to find and review later.
This would solve the "crap, I wish I had been recording" problem, and it would also solve the "which of the 14 sorties that I recorded tonight was the good one" problem.