It's common knowledge at this point that Robert Downey, Jr. doesn't have much time left on his Marvel contract (although it was never supposed to include Civil War or Spider-Man: Homecoming). The question is what will Marvel do with Iron Man when RDJ retires? Recasting what is arguably Marvel's most iconic cinematic character would not go down well at all, so the sensible play is to have a different character take over the Iron Man mantle. The best person for that job is 15-year-old Riri Williams.
Riri is a new face in the Marvel universe. So new, in fact, that she won't be making her official debut until this November's Invincible Iron Man #1. She's a 15-year-old science prodigy who has reverse-engineered her own version of Tony Stark's Iron Man armour, and will officially take his place when he steps down.
With the rate that Robert Downey, Jr. keeps extending his contract, it is impossible to tell when or even if he's going to step down as Tony Stark. If/when he does, Riri Williams would be the perfect choice to continue the franchise. Who knows, she could even be a classmate of Marvel's greatest acquisition to date - Peter Parker.