D23 Expo 2019: She-Hulk's introduction suggests MCU's next wave of films and shows will deal with legacy as the main theme
'She-Hulk' will be making an entry into the MCU. This surprise announcement was made during the D23 Expo 2019 and after seeing Professor Hulk in 'Avengers: Endgame', we get to see a new superhero with similar, but more powerful abilities than Bruce Banner's green-rage monster. In introducing She-Hulk, Marvel may also have teased that there is a new breed of superheroes ready to suit up and save the world. After all, the Avengers have gone their separate ways after 'Endgame'.
This is the third instance where we see the baton being passed. Steve Rogers (Chris Evans) passes his shield to Sam Wilson aka Falcon (Anthony Mackie), Iron Man (Robert Downey Jr.) did something similar with Peter Parker (Tom Holland) in 'Spider-Man: Homecoming', Clint Barton aka Hawkeye training his daughter, Kate Bishop to be the next skilled archer, and now She-Hulk gets ready to go into savage mode, courtesy her cousin, Banner.
Before going on to become a green monster (some comics say her transformation was permanent), She-Hulk was Jennifer Walters, a lawyer. Following a critical injury, she receives an emergency blood transfusion from Banner, acquiring a milder version of his Hulk condition. As such, Walters becomes a large, powerful green-hued version of herself while still largely retaining her personality.
In particular, she retains her intelligence and emotional control, although, like Hulk, she still becomes stronger if enraged. It does make sense to bring in She-Hulk as Banner's replacement if Marvel has plans to make another Avengers movie. With the OG avengers more or less gone, MCU may form the New Avengers and we may see She-Hulk joining the ranks of Captain Marvel, Black Panther, and Dr. Strange. Also, with Banner now missing an arm he would probably not be of much assistance anyway.
Coming back to the older heroes paving the way for new ones, the next wave of films and shows have been dealing with aspects of legacy and could eventually lead up to another mega film like 'Endgame'. At this stage, it remains to be seen if we see Mark Ruffalo reprises his role as the Hulk in the series. If he does, the legacy concept will most definitely hold true.