Tony throws the line back at Steve in the beginning of Endgame when he’s distraught about their dire situation, and now every time we see this Ultron scene, it’ll have an extra special connection.
The scene has a special significance now because of Tony calling the mysteries in the sky their “endgame,” which he created Ultron at the time to fight off and Captain America saying they can take anything down together.
It is crazy to imagine that just a few months ago we were theorizing about Avengers 4 titles, and it ended up being right under our noses in Age of Ultron.