I don't see how any of this would improve the game.
1. smoke & flames in the cockpit
We have smoke and flames. Flame mean you have a short time before blowing up. How would " in the cockpit" improve the simulation, same outcome. Smoke and flames in the cockpit would kill the pilot, and pilot death is in there now. The books I read, oil on the windshield was more of a problem then smoke. Smoke would be more of an issue in bombers that don't have a canopy.
2. flight control damage (I know we have missing controls etc... but how about the damaged controls, fluttering ailerons etc...
We have flight control damage. What is the difference missing a control surface, or missing the cable (or line), that controls it? Same thing. How do you simulate fluttering controls without force feedback sticks? If you do, what difference would it make. The plane is controllable with skill you can land it, or it isn't you bail or crash.
3. engine damage, over heat cowl flaps etc....
We have engine damage an overheat, the engine quits. I think HT said long ago this is an air combat simulator. Detailed tasks for basic flight are automatic. That is why we have combat trim, and auto switching of fuel tanks.
4. loss of oxygen effects... i.e. over 10k and you forget to switch to the oxygen and you pass out etc...
See 1,2 and 3 above. Most people don't fly much over 10K anyway. Most of the fighting is below 10K, or quickly falls below 10K. Again, maybe bombers. This would also be more of an annoyance, like forgetting to fill the tanks full, get to the fight and the engine quits. When this happens to me, I don't say " Oh, cool simulation, I forgot to fill my tanks and now I am going to die!"
Gunner