Natalie Portman is an amazing actress and I think she could do a lot with this role. In the comics, Jane Foster is diagnosed with cancer when she takes Mjolnir and becomes Thor - if they choose to adapt that storyline, well, someone of Portman's caliber could definitely do that justice. I expect the film to be hilarious too: Taika Waititi's sense of humor is great. I hope they get Jeff Goldblum back. I love that they're going to openly embrace an LGBTQ storyline with the character of Valkyrie, and whomever her "queen" turns out to be - Carol Danvers? Supposedly, the film could also introduce the first transgender superhero to the MCU. There's a good chance Loki will be back. Yeah, I'm in.
I'm glad there will be a fourth Thor movie but only if the writing is good and the focus on gimmicks like Jane-as-Thor doesn't give me a lot of hope for that. While this has become canon in the comics, that's only because the comics have degraded so badly into agenda-driven storylines under Marvel's current leadership. Note that this particular storyline in the comics was also a gimmick and it didn't go over well with the comic fandom.
I love both the performance of both Hemsworth and Portman and thought they did well together in the first Thor movie. I would have welcomed a reprise with them anyway but was put off by Taika Watiti's reaction to the fandom not being enthused by this gimmick.
I will see "Black Widow" because hey, it's ScarJo but as far as I'm concerned, the MCU died with Tony Stark.