The Marvel Cinematic Universe is known for using post-credits scenes to foreshadow future films, resolve a plotline from the film or provide comic relief. However, not all films have 2 post-credits scenes. And they would not know what they were doing with these characters during that time... most of it is changed to whatever the script wanted them to be... or not cast/planned earlier.
The post-credits scene scenario began when Nick Fury appeared at Tony Stark's mansion and informed him that there were more superheroes like him before talking to him about recruiting Iron Man for the Avengers Initiative. Since then, post-credits scenes have become a recurring staple in the films of the Marvel Cinematic Universe. And when the 2012 Avengers film was released, they had 2 post-credits scenes for the first time. This has become very common with most films of the MCU, though Iron Man 3, Avengers: Age of Ultron and Avengers: Infinity War only had one post-credits scene.
However, if they were to come up with 2 post-credits scenes of these films, they would foreshadow the first Ant-Man film, have the elevator joke from Age of Ultron and foreshadow Hawkeye and Ant-Man's roles in Avengers: Endgame. Their absence from Avengers: Infinity War has caused fans to troll Marvel for refusing to show the heroes at all. If they appeared in the mid-credits scene, fans would be glad to see the retired SHIELD agent and former criminal-turned-superhero in Marvel's biggiest film to date, even if it was for one scene. So my predictions for them would be this:
Iron Man 3: Cross Technologies is having a meeting with Arnold Brown(portrayed by Peter Sarsgaard). The scene opens with Brown entering the board meeting with Darren Cross's employees. One of the employees tells Brown that they have started working on "the suit". He remarks that Mr. Cross's old mentor(Hank Pym) could never trust him with "the secret" he kept from him. Brown says no-one can ever convince him to trust them with his "particles from another dimension". Then, Brown states soon as the suit is completed, their boss will plan to sell it to the Ten Rings and "an old terrorist organisation", hinting HYDRA is still active in some form.
Avengers: Age of Ultron: When Thor returns to Earth for a brief visit, he gives Mjolnir to Captain America, Tony Stark and Vision. They come across an elevator to see if it is worthy of going up. When the door closes in front of them, Cap,Tony and Thor seem shocked while Vision isn't surprised. Tony says he was right about the elevator and Cap says when he tried to pick up the hammer, he thought that he would have the power of a god and he always wished he was worthy of Mjolnir as a nod to the comics where he eventually became worthy of wielding the hammer. Tony says he got the idea of creating Ultron from one of Dr. Hank Pym's projects as a reference to the fact that Hank Pym was the creator of Ultron in the comics. Cap then says "Damn it" and hands Tony 10 bucks. The scene ends with Tony saying "Language!"
Avengers: Infinity War: Clint Barton(Jeremy Renner) is chopping wood and enjoying his retired life, quipping to himself if any "bad shit" happened to his family, he would never find another woman like Laura(Linda Cardellini) and he would rejoin the Avengers as "a Archer for Life". But then suddenly, he hears a scream. He sprints inside the house, and he sees something he can't possibly ignore: his wife holding two of his children, who are disintegrating, while the other runs up to him and disintergrates right in front of him. He then makes eye contact with his wife and passionately kisses her as she disappears as well. And then he falls to his knees and screams at the loss of his family. Another mid-credits scene features a comedic scene where sometime before the mid-credits scene of Ant-Man and the Wasp, Scott Lang(Paul Rudd) is trying to start Luis's van when suddenly it breaks down. He lifts up the front axle and realises that the front engine has broken down. As he fixes it, he calls Hank Pym who tells him he's on his way to help him collect "the energy". These scenes would not only foreshadow Avengers: Endgame, but have Hawkeye and Ant-Man at least somewhat involved in one scene before Avengers: Endgame and would also be a reason for Hawkeye coming out of retirement. As I said, one of the ending scenes with Ant-Man would also take place sometime BEFORE the mid-credits scene of Ant-Man and the Wasp while building up Ant-Man's role in Avengers: Endgame and not spoiling much of the events of Ant-Man and the Wasp.
Please let me know what your thoughts are on these MCU films having 2 post-credits scenes?