In Avengers: Infinity War fans learnt that one needs to sacrifice their most loved thing in order to attain the Soul Stone. Following which, a million of hearts were broken when Thanos chose Gamora for the sacrifice. But a million more hearts will be broken when Iron Man will have to make sacrificial choices to save the universe in Avengers 4.
Connecting Tony Stark and his sacrifice choice, the first things that come to our mind is his love interest Pepper Potts or his longtime friend Steve Rogers aka Captain America. But, the Reddit user who initiated this theory has envisioned a more logical scenario for Tony.
The user suggests that Iron Man will time travel to 1991 and infiltrate Hydra or seek out the Winter Soldier and order him to hit his parents himself. Explaining his theory, the user wrote, "Knowing all the while what it(sacrificing his parents) will cause in the future and all the anguish it will personally cause him along with the events of Civil War, breaking up the Avengers, and everything that happens after that."
He further added, "Or maybe Nick Fury back in 1991 tells Tony that he has to do this. It would be the hardest decision that any character has had to make in the entire MCU, and a decision that only Tony Stark himself could make, a burden that only he could bear, truly exemplifying him as "Iron" Man."
It appears to be realistic because Captain America: Civil War is based on the conflict between Iron Man and Captain America over the death of Tony's parents. Tony Stark is heartbroken because Steve Rogers knew that Bucky Barnes killed his parents and he kept it a secret.
The Nick Fury part also makes sense because at the end of Infinity War, before disintegrating into dust, he was the one to make the final call to Captain Marvel. Thus, there are chances that he already knew what the situation will lead to and he was prepared.
Will Iron Man time travel and will he sacrifice his parents for the Soul Stone? Well, the fans will find out in May, next year, when the concluding film of the Avengers Universe will hit the screens.