The following contains spoilers for Black Panther. Go check it out, then come back and read this.
While little is known for sure, the expectation is that the end of the Marvel Cinematic Universe's Phase 3 will also be the end of Robert Downey Jr.'s run as Iron Man. However, the newest MCU film may have given us an idea how the hero, if not the man, could continue. The MCU would certainly be lacking if it lost its super intelligent, super creative, tech genius with a super fast wit. Luckily, Black Panther introduces us to another character who fits that description perfectly. The title character's sister, Shuri, played by Letitia Wright, could fit nicely into the gap that Robert Downey Jr. would leave behind. She's the perfect character to take over as a new Iron Man, or if that's not the plan for her, she could help locate the person who could.
In Black Panther, Shuri is the young sister of T'Challa, and while she's young, she's the smartest person we meet in Wakanda. She's in charge of all technological development in the nation, and appears to be personally responsible for many of the innovations that we see, including the ability to transfer vibranium by high-speed rail and create a Black Panther costume that can be hidden inside of a necklace. Part of Tony Stark's role within the Avengers has been to act as the creative spark and the financial backing for the team. Shuri clearly has the ability to do the former, and with the nation of Wakanda behind her, the latter shouldn't be a problem either.
We already have reason to believe that Shuri and Iron Man may end up working together as early as Avengers: Infinity War. In the TV spot for Infinity War that aired during the recent Super Bowl, we saw Tony Stark wearing an Iron Man suit that appeared to build itself around him as he moved. Check out the ad again and watch the suit as he removes his glasses.
The way the Iron Man suit is acting here looks a lot like the way the Black Panther suit forms around T'Challa in Black Panther. It's quite possible that the newest Iron Man suit that Tony will have in Avengers: Infinity War is actually built by Shuri rather than Tony. Or at the very least, Stark built it using her technology now that Wakanda has revealed itself to the world. If it is Shuri's tech, she'd be the best person to throw it on and use it if, for any reason, Tony Stark is unable to do so going forward.
We also see in Black Panther that Shuri is a strong fighter. She doesn't hesitate to take the fight to Killmonger at the end and while she may not be able to take him down herself, it's nothing that a little more training and a suit of metal wouldn't fix.
Finally, Shuri has the wit. The moment where people think she might try and challenge her brother for the throne, but she really just wants to complain about the ceremonial outfits, is the sort of thing we'd expect out of Tony Stark in a similar situation. If you're going to be a superhero, you need to know how to banter.
There is another possibility, which is that Shuri herself might not become Iron Man, but she could discover the person who does. At the end of Black Panther, we learn that Wakanda is going to begin building outreach centers throughout the world, with the first being built within the Oakland, California inner city. Shuri is going to be placed in charge of these centers, which means that she'll be in a position to notice when somebody comes in showing a high aptitude for this sort of technology. Somebody like an African-American teenage girl named Riri Williams.
In Marvel Comics, Riri Williams is a young girl who builds her own Iron Man-style armor and goes by the moniker Ironheart. She essentially replaces Iron Man for a time, so there's a precedent for such a thing to happen in the MCU as well. Obviously, as has been the case since the beginning, the comic storyline wouldn't be followed exactly on screen, but it's possible that something similar could still take place. If there is an interest in introducing Riri in the MCU, these outreach centers would be the perfect place to do it.
At some point, whether it happens during Avengers: Infinity War or after, Robert Downey Jr. is going to hang up the Iron Man suit. While the character may be gone for a while, just like with the comics themselves, it's unlikely the character is going to be gone forever. And yet, unlike the comics, once Tony Stark leaves the MCU, he's almost certainly not coming back, which means Iron Man is going to need a new pilot.
Shuri is the perfect choice because, while in some very obvious ways she's quite different from Tony Stark, the character also shares a lot of similarities with him, meaning that some future Iron Man movie will still have a lot of the same flavor that people remember from previous entries in the series. Whatever direction a path to a new Iron Man takes, there's a very good chance it will go through Shuri. That's not a bad thing; the more we see of her going forward, the better.