As it was pointed out before, pilots already have values like stamina and stuff like that. If you maintain medicore G you are likely to black out as well as if you make a high-G-turn. Also if you already blacked out in a given time before, it's more likely you black out again.
All this is just superficial, granted, but I'm pretty sure that if fatigue is modeled for the aircraft the pilot will not be forgotten.
Just because nothing like that was posted as a definite statement, yet (at least afaik), doesn't mean it won't be there
Just don't expect a healthbar or something.