You know, I love it when the MCU lands big, serious actors. I mean, superhero movies on the whole don't have a problem hiring all sorts of actors, from A-list to Oscar types, like Viola Davis and Will Smith in Suicide Squad or Benedict Cumberbatch for Dr. Strange or Jeff Bridges in Iron Man, but occasionally there's a bit of old school casting that makes me sit up and take notice.
Gary Shandling in Iron Man 2 was the first one. I just never pictured a world in which Larry Sanders himself would be on screen with Tony Stark. Kurt Russell in Guardians of the Galaxy Vol. 2 was another happy surprise.
The biggest get up to this point was Robert Redford in Captain America: The Winter Soldier. Him being the big bad guy of that film helped Winter Soldier set a new tone for the MCU. It's still got goofy comic book shit in it (the whole Zola/Talking Computer sequence for instance), but there's a degree of legitimacy that comes with someone like Redford.
It seems like Captain Marvel is going in that same direction, at least in terms of casting. The Hollywood Reporter has a story saying that Annette Bening was cast in a secretive role that is most likely a scientist of some sort.
Bening doesn't do a lot of giant budget movies and when she does they tend to be weird. Mars Attacks jumps to mind. Her big films all seem to be awards stuff, like American Beauty. She usually stays in the more serious adult drama world so when she signs up for something like Captain Marvel that tells me she believes in the story being told and/or really wants some of that sweet, sweet comic book movie money.
Either way it's an exciting development for MCU fans.