We've officially reached a point where spoilers regarding Avengers: Endgame are allowed, and that means that the filmmakers themselves are now talking openly about some of the decisions that led to what we saw in the epic Marvel movie. They're also talking about decisions that led to things that ended up not making it into the movie at all.
Several months ago it was reported that 13 Reasons Why and Love, Simon star Katherine Langford had been cast in an undisclosed role for the recent film. However, if you've seen the movie, you know the actress never actually appears in the final film. While the scene was cut, it seems the plans for Langford were significant, as she was hired to play an older version of Tony Stark's daughter, Morgan Stark. According to Joe Russo...
There was an idea that we had that Tony was going to go into the metaphysical way station that Thanos goes in when he snapped his fingers. And that there was going to be a future version of his daughter in that way station.
When Thanos commits universal genocide at the end of Avengers: Infinity War, we see him standing in some sort of otherworldly place where he is confronted by a child version of Gamora. She asks him what it has cost for Thanos to finally achieve his objective.
It seems the plan was to have a similar scene in Avengers: Endgame where Tony Stark has a similar vision upon using the Infinity Stones. Instead of seeing his younger daughter, he sees a version of her grown up, where Morgan tells him that it's ok that he's gone. This gives Tony Stark peace and allows him to go.
The Russos confirm to the Happy Sad Confused Podcast that the scene was shot, but in showing it to test audiences, they found that the scene was actually quite confusing, and so they took it out. Anthony Russo explains part of why it didn't work.
What we realized about it was we didn't have, we didn't feel an emotional association with the adult version of his daughter so it wasn't ringing to us, resonating with us on an emotional level, which is why we moved away from it.
Instead, Pepper Potts is sitting by Tony as he fades away, and tells him that she and Morgan will be ok. Allowing Tony to finally rest.
Since the scene was shot, there's the possibility we might end up seeing as part of extras on the eventual Blu-ray release for Avengers: Endgame. While the scene might not have worked in the final cut, that doesn't mean it's not a cool scene on its own.
Of course, this information does open up a couple of questions we have to ask. If using all of the Infinity Stones sends you to some sort of cosmic way station, what did Hulk see when he was there?
Secondly, if the Marvel Cinematic Universe ever decides to take a time jump forward and show us an older Morgan Stark, could they call Katherine Langford again? Assuming Morgan got her parents' brains, she could be an important character in the future of the MCU.