The biggest upside of the current MCU is how the characters are intertwined between one another. Even if the first 2 Avengers achieved that integration well, I feel like Infinity War will be the first time establishing an even bigger universe with all the characters from Phase 3. That is why my end credits scene will be introducing the first interaction between a few fan favorites.
As a post credits scene of Infinity War: Part 1, I think we should combine...
Iron Man and
The Guardians of the Galaxy
Lead Up to the Post Credits
Now before we get into the post credits scene itself, we all need a bit of a backstory. I believe that the end of Infinity War: Part 1 should be a battle between the Avengers and Thanos that ends horrible for Earth's mightiest heroes. I would like to stress that, if I were an exec at Marvel, Guardians of the Galaxy 2 would end with the Guardians heading to Earth, after hearing of Thanos' plan. In order for this to make sense, the Guardians would have to have NO CONTACT between them and the Earth Heroes of the MCU. I know that might sound like torture, but trust me. It's worth it. If any fellow Marvel buffs are familiar with the Infinity Gauntlet event, I would like to stage it much like it was in the book. Thanos decides, due to his cockiness the power of the gauntlet gives him, that he should fight his enemies instead of using the Gauntlet to just snap them out of existence. He takes all the gems besides the Power Gem off of the Gauntlet and prepares to square off against the team. Iron Man, being equally as cocky, decides to lead the charge head on against Thanos. He charges up his repulser blast, ready to strike, but all we see is Thanos' Gauntleted hand extend and grab onto Tony Stark's arm. A surprised Tony is quickly trapped as Thanos grabs Tony's head with his hands, really to use the Power Gem to smash his head at any moment. All the Avengers stay still, scared that any movement will trigger Thanos' wrath. Quick cuts reveal the surprise of other Avengers as Thanos leans to a struggling Tony, who is no match for a Powered up Thanos. Thanos whispers to Tony-
"When will you humans ever learn? You can't stop the Mad Titan. Your Earth will die. Your friends will die. But you will be the first of many"
Thanos then takes Tony and uses the Power Gem to hurl him into space. Iron Man is out of sight as Captain America screams, with pain in his eyes, that they must defeat Thanos before it's too late. They cannot spare a fighter to go after Tony. He would be the first casualty in a fight that ends Part 1. The credits roll towards the end of the battle when Thanos, in one swipe, shatters the shield of Captain America after defeating nearly everyone else. All is lost.
Post Credits Scene
Now comes the fake out. The Post Credits scene starts with a full shot of the Iron Man suit floating through space. Tony is seen, in a close up, as his AI is giving a damage report and is counting down till oxygen runs out for Tony. Tony closes his eyes and accepts his fate. His suit is down and he is running out of oxygen, all while Thanos is more powerful than ever. The shot moves back to full shot of the whole suit as it powers down. The light of the suit shuts off as the viewers think this is one big sendoff for Tony. Suddenly, a light off screen shines on the suit. The sound of rockets go off as a masked Starlord grabs the suit, with Tony inside and flies offscreen. You hear a ship door close and it flying away as the scene goes dark. That's how Part 1 should end.
Why this ending?
Simply put? It's an amazing reveal that leaves a lot of question for Part Two. Did Starlord get there in enough time to save Tony? What are they going to do with him? Will they be able to get back to help the Avengers? All of these would create even more hype for Part II, which Marvel can't get enough of. This would also allow for there to be interactions between the Guardians and Iron Man without the rest of the giant cast getting in the way. I demand witty banter between Rocket, Starlord and Tony! And, due to Tony being a Guardian in the comics, it would create a second wave of heroes to save the heroes of Earth that were defeated by Thanos. Everything adds up and everyone is happy!