10 Major Details Marvel Just Revealed About Thor: Ragnarok
3. Natalie Portman And Stellan Skarsgard Aren't
As was actually confirmed before Kevin Feige's official data dump on Ragnarok, Natalie Portman won't be back to play Jane Foster. Feige himself confirmed as much, saying it came down to the fact that the film won't be set on Earth for the majority, and to be fair, having too much focus on the human cast was one of The Dark World's biggest problems, so it's forgivable.
At the time she was confirmed as being out, Tessa Thompson was rumoured to be playing Thor's love interest, and the confirmation of Valkyrie does suggest there could be a new romance on the cards. It's a shame for Portman, but her character was gradually being pushed out of relevancy in the franchise anyway. A fresh start is a positive thing.
As for Selvig, Skarsgard confirmed that he too will be taking a break, though he did suggest he's back for Avengers: Infinity War. Hopefully to do more than hold Thor's towel this time.