The Incredible Hulk is an important movie that many ignore in their MCU rewatches. That was certainly seen back during Infinity War and Endgame where many sites posted MCU rewatch instructions and completely ignored the MCU Hulk film. But it not only introduced the Super Soldier serum from Captain America: The First Avenger, but also the MCU’s Thunderbolt Ross.
Marvel has since brought back Ross as an antagonist in Captain America: Civil War and Avengers: Infinity War (and he was at Tony’s funeral in Avengers: Endgame), and we’re going to be seeing a lot more of him in the future. He’ll cameo in Black Widow in May, and it sounds like he’s destined for a much bigger, and red, role soon.
According to Daniel Richtman, Red Hulk is indeed slated for a role in a future MCU movie. He does not say it’ll be in She Hulk, it’s entirely possible it’s being saved for the Thunderbolts project that’s in development. All he says is that it’s an “upcoming project” so it could be anything Marvel has in the works.
Red Hulk’s origin in the comics involves Ross taking the serum, and becoming the thing he hated the most; a Hulk. It’s likely his MCU origin will be similar, as we saw he was experimenting with the Super Soldier serum all the way back in the often-ignored The Incredible Hulk.