Karen Gillan's Nebula had a good amount of material in Avengers: Endgame -- even beyond that fun game with Robert Downey Jr., which was apparently improvised. But she could've done even more, and it would've been a great nod to Nebula's Marvel Comics story from The Infinity Gauntlet.
There's more than one Nebula featured in Avengers: Endgame, thanks to time travel, and concept art from the movie shows 2014 Nebula wearing the Infinity Gauntlet -- as Rocket Raccoon watches from below.
Check out the concept art by MCU artist Stephen Schirle:
That is pretty epic. The companion book for Avengers: Endgame already revealed that another version of the script had Nebula wielding the Infinity Gauntlet -- and apparently things didn't end well for her:
While the Nebula from the past was killed by her future self in Avengers: Endgame, her demise was scripted a lot differently in another version. In that draft, she was able to intercept the Stark gauntlet during the massive game of keepaway in the film’s final battle. Wanting to prove to her father Thanos that she is a capable and strong warrior, Nebula tries to use the glove herself– a nod to the 1991 comic book series Infinity Gauntlet, written by Jim Starlin. This Nebula learns she is not powerful enough to use the Stones and survive.
In the final cut of Avengers: Endgame, only Thanos, The Hulk, and Iron Man wielded the Infinity Gauntlet. It gave Hulk what we've been told was permanent damage. And its power ultimately killed Iron Man. But Nebula -- in the comics, Nebula managed to take the gauntlet from Thanos to restore her wounds. Check out THAT look:
Nebula was first introduced in the Marvel Cinematic Universe through Guardians of the Galaxy. She was an antagonist alongside her "sister" Gamora, another child of Thanos. Nebula had quite a powerful arc from Guardians 1 and Guardians 2 to Avengers: Infinity War and Avengers: Endgame. As Karen Gillan teased before Endgame, fans ended up rooting for Nebula. She and Rocket ended Infinity War as the last two Guardians standing. The Nebula of Avengers: Endgame's present killed her own 2014 counterpart, but by the nature of Endgame's time travel rules, that didn't launch a universe-shattering paradox or anything like the fears from Back to the Future.
Now that James Gunn has finished filming for The Suicide Squad, he should be turning his gaze to Guardians of the Galaxy Vol. 3. Once that movie starts filming later in 2020, it'll arrive in theaters ... eventually. Marvel doesn't have an exact release date yet.