I have something that I want to happen with AOS actually, but half the people here will disagree, to other half will start sending death threats. I'll give it a shot anyway.
I want them to some version of the New Avengers after Phase 3. They have plenty of characters to choose from and form a solid and diverse team. They've set up perfectly the Cap replacement (would prefer Bucky in that place, his relationship with Steve is much deeper and Sam's character is not really captain-y to me).
Steve gets killed by Thanos (huge moment since it would finally raise the stakes in these movies) and Tony, after all that happened previously with them, hangs the suit.
He's traumatized but still wants to help so they make him head of Shield.
It solves so many problems: MCU revolving around Iron man, Robert's age, the need for fresh characters and stories, and since the tv show will end by then, you can put it into the background of the movies and still use the acting chops that Downey has.
Maybe it would be weird for his comic book version, but here he's already a part of the government.