The arm being still in the sling could just speak to the amount of damage that had been done, & the change in appearance will supposedly be addressed in the SHE-HULK series on Disney+.
The idea I've heard floated is that if Banner has a large role in
She-Hulk, they can't afford to have him spend the entirety of his screen time as Hulk on the TV budget, and so will have to come up with a story reason why he no longer spends all his time that way. Another idea, at least for me, is that I have wondered ever since
Endgame where they would go with the Hulk as a character moving forward. I enjoyed seeing the character as Professor Hulk in that film, but I don't think he's as appealing long-term without being a "rage monster" at least some of the time. The way he was used in the films between
Avengers and
Thor: Ragnarok was one I really liked, where it seemed that if Banner brought him out willingly, he was able to do more strategically-targeted smashing as opposed to the more indiscriminate wanton destruction that seemed to result when Banner changed against his will. And really, who among us hasn't been able to sympathize with Banner wanting a normal life, while also secretly wishing we had the Hulk at our disposal at times? That's what makes him such a beloved wish-fulfillment character for kids, who have so little power. But the half-hearted smashing we saw in the return to the Battle of New York in
Endgame was not something I really want to revisit so much, at least not without exploring the idea of what it would take to drive
that version of the character to "Hulk smash!" mode.* They had been making Hulk a bit smarter in each appearance, with him being a relative motor-mouth in
Thor: Ragnarok as compared to his earlier appearances. I like that. I'd just like to see him continue to have to struggle to maintain control to some degree.
Some have also suggested that what we're seeing may be laying the underpinning, long-term, for the "Maestro" character from the
Planet Hulk storyline, while Phase 4 may be building to some sort of adaptation of
Secret Wars.
*And they
did sort of hint in that direction in
Endgame a couple of times -- first, his reaction when Thor grabbed him early on, and later when he hurled the bench across the lake in frustration.
SSB