A scrapped plan for Captain America: Civil War would have changed the MCU Hulk arc. Unlike many of his fellow Avengers, Hulk hasn't had the chance to star in multiple solo installments. Instead, he became a team player in the Avengers movies and a ing character in other heroes' stories such as Thor: Ragnarok and She-Hulk: Attorney at Law.
Nevertheless, Hulk has evolved quite a lot since his MCU introduction in 2008's Thor: Ragnarok, where Hulk evolved off-screen; as well as during the Blip, where Smart Hulk came to life. The rest of the Avengers didn't get to witness these changes firsthand, as most of them were busy fighting each other during the events of Captain America: Civil War or blipped away by Thanos after Avengers: Infinity War.
An early Captain America: Civil War concept had Thunderbolt Ross transform into the famous Red Hulk. Directors Joe and Anthony Russo revealed that they considered adding both the ultimately cut Red Hulk and Spider-Man's Iron Spider suit (via ComicBook), but they scrapped the idea early in the process so as not to oversaturate the already crowded movie. Indeed, Colonel Ross' transformation would have taken up a considerable part of the story, though it would have also affected Hulk's MCU journey in his following appearances, requiring him to acknowledge the existence of another Gamma-powered monster and giving him a more center-stage role via this storyline.
How Red Hulk Would Have Changed Hulk's Arc
Not only is Marvel's Red Hulk an angrier version of Hulk, but also his long-time enemy. Colonel Ross held a grudge against Bruce Banner since they met, and he considered Hulk to be a mindless living weapon. By becoming a monster himself, he could have endangered innocent lives just like he did when he turned Emil Blonsky into the Abomination, causing Hulk to intervene and relive the events of The Incredible Hulk, this time with a more unpredictable villain. The birth of the Red Hulk could have also led Bruce Banner to rethink his transformation into Smart Hulk. Perhaps Bruce Banner would have pursued it earlier than Avengers: Endgame in order to find a cure for Colonel Ross - or what's more likely, he would have ditched it to fight Red Hulk.
Part of the reason Bruce Banner was able to become MCU Bruce Banner might not have been present in her cousin's accident, which would have prevented her own transformation.
The conflict between Hulk and Colonel Ross' Red Hulk would be worthy of at least one movie, but unfortunately, it is unlikely to materialize, as Colonel Ross actor William Hurt ed away in early 2022. This said, given the sheer roster of different Hulks within the comics, it's not impossible to imagine a similar conflict could arise in the future. Bruce Banner and Colonel Ross never had the chance to interact directly after the events of The Incredible Hulk, but in the end, Red Hulk's absence ends up being beneficial for Bruce Banner, whose only worry for now is training Jennifer Walters.
