Newly released Avengers: Endgame concept art features Nebula wielding the Infinity Gauntlet. Karen Gillan's Nebula ended up having a pretty large part in both Infinity War and the last installment. Her storyline was changed up quite a bit from the comics, which was to be expected since Marvel Studios never does a true adaptation of the comics for obvious reasons. With that being said, it looks like screenwriters Stephen McFeely and Christopher Markus may have originally wanted to follow Nebula's comic story arc a little closer.
In the Avengers: Endgame concept art, Nebula takes on the Infinity Gauntlet as Rocket Raccoon looks at her from behind a rock. It's uncertain, but this may have been meant to take place during the final battle scene with Thanos on the charred and cratered remains of Avengers HQ. She is obviously in some pain as the power begins to surge through her. It's entirely possible that one of the original plans was to have Nebula take out her father, instead of Tony Stark.
Avengers: Endgame and Infinity War were planned out years in advance, though changes were made throughout that time. Having Nebula take on the Infinity Gauntlet may have been in the running for a time, or it may not have been seriously considered at all, though early rumors suggested that she would be the one to take down Thanos with the help of Gamora. In the end, the Russo Brothers, along with Stephen McFeely and Christopher Markus, decided to take the movie in a different direction, which had Tony Stark making the ultimate sacrifice to save the universe.
Nebula and the Infinity Gauntlet goes back to the comics. Thanos had her in zombified state while he took on the gauntlet for himself and defeating Eternity. Thanos then expanded his consciousness into the universe, leaving his body comatose. It's at this point in time that Nebula was able to gather the strength and get to the Infinity Gauntlet. She was immediately revived and now the most powerful person in the universe at the same time. She banished Thanos to the universe and then took it over. The next storyline involved the Mad Titan joining up with some heroes to take her out.
Other images in the set reveal Nebula spying on the Black Order, along with Thanos meditating with his damaged arm in front of the destroyed Infinity Gauntlet, while the Avengers look on. There's another image of Smart Hulk meeting one of his young fans, which looked much different on the big screen. There seems to be a wealth of unused concept art from Avengers: Endgame floating around.
It would have been pretty wild to see Nebula take on the Infinity Gauntlet in Avengers: Endgame, but the story in Infinity War didn't allow that to happen. Instead, Nebula proved herself to be just as heroic as we've seen in the past as she tried to convince the Gamora from past that they are currently friends and on the same side. That's a story that will have to be explored further in Guardians of the Galaxy Vol. 3. Thankfully, James Gunn already has that all figured out. You can check out the latest concept art from Avengers: Endgame below, thanks to the Marvel Studios Movies Twitter account.