This is an interesting idea. Yes, it has been mentioned before, but perhaps it could be modified just a bit. I don't think there should be random failures in the Main Arena (MA). The MA is not the slightest bit about realism (in terms of recreating WW2). It is about a no-holds barred team free-for-all. As AH2 is developed, it seems as if the MA will be for the fun and practice of what is to come in the Mission Arena (MisA).
Now, the MisA seems to be about recreating the feel of WW2 and the missions/battles that occurred during the war (i.e. bomber raids on Berlin, carrier battles in the Central Pacific, etc.). If there was an arena setting that would enable random failures in one arena but allow them to be disabled in another, I would be all for it. Failures of non-critical systems would be cool.
To be clear, let me use the F6F-5 as an example (only because I know more about it than other planes in the game). Failures of certain systems that are non-critical, but could affect how you fight could include:
1) Failure of WEP
2) Failure of supercharger to shift into high blower - reduced hi-alt performance
3) Gun jams
4) tail hook failure (may have to add the barracades to the decks of the CV's)
5) gunsight failure (no sight image)
6) instead of engine failures, maybe some kind of reduced performance of the engine or "rough" running engine.
Anything along those lines that will not keep the plane from fighting but could or can change the way it is fought and allow the pilot to return to base. Keep in mind, this is completely seperate from any kind of battle damage (i.e. damage could kill the engine whereas a random event would not)
Again, this could be something that could add to the realism of the MisA without keeping someone from actually flying or taking part (as an outright engine failure would be). When it comes to the MA, though, I think it would be an incredibly bad decision to implement something like this there.
Oh well, just my thoughts on this topic. Take it for what its worth (not much, I'm sure).
-math
