The Red Hulk might be seen in 'She-Hulk' or even as part of the Dark Avengers at a later stage
The Hulk has already made an appearance in the MCU and has been an integral part of the Infinity Saga. The D23 Expo also saw Marvel Studios announce the entrance of 'She-Hulk' into the fold and fans are now hopeful that the Red Hulk may soon make an appearance as well. The Red Hulk's appearance dates back to 2008's Hulk #1 and was a lot different than the Hulk we have seen. The crimson hue, the intelligence, the combat training were some virtues that were seen in the smart Hulk after a really long time.
It was eventually revealed that the Red Hulk was General Thaddeus "Thunderbolt" Ross. The character has made appearances in 'The Incredible Hulk', 'Captain America: Civil War' and 'Avengers: Infinity War'. In comics, Ross acquired his powers through a combo of cosmic and gamma rays by the Intelligencia and A.I.M. so that they could have a better response should the green Hulk go on a rampage and take them on at some stage. After the story that introduced Red Hulk, he became a sort-of ally to Marvel's heroes. He briefly joined the Avengers and organized a new incarnation of the antiheroic Thunderbolts.
As far as appearances go, the Red Hulk may most likely make an entrance in 'She-Hulk'. Marvel seems to already have an answer to 'Suicide Squad' as they have already introduced a few anti-heroes in Ghost ('Ant-Man and the Wasp') and US Agent ('The Falcon and The Winter Soldier'). Assuming there is a Dark Avengers movie in the works, probably by phase 5, there's a very good chance the Red Hulk may come smashing in.
Co-writer Stephen McFeely revealed they almost considered introducing Red Hulk in 'Avengers: Endgame' at one point. In an interview with Backstory, the writer was asked about the scene in which Hulk's skin burns with a red glow after wearing the Stark-made gauntlet and whether it was a sign they considered bringing in the Red Hulk in the movie.
McFeely, however, had considered the possibility for a day before scrubbing the idea. He explained that their version of Red Hulk would have been different than the comic book incarnation and would not have been enough of a change for Bruce Banner: "Red Hulk is a completely different thing in the comics. It wound up being, well, really we’re just saying he changes color. That’s not a character change. If there’s a future for William Hurt as a superhero, he can turn into Red Hulk."
What are your thoughts on the Red Hulk making an appearance in Phases 4 or 5?