Among a plethora of early additions to the Marvel Cinematic Universe, Marvel Studios and Disney's ability to nab Natalie Portman was one of the most impressive. Sure, they had cast other big name stars, but Portman would be riding high off her Oscar win from Black Swan by the time Thor hit theaters. Her role as Jane Foster however did not receive the reception that all parties involved had hoped for. This is not because of Portman's performance, but instead due to Jane's role largely being to keep Thor on Earth.
This will not be the case in Thor: Ragnarok however with Jane not set to make an appearance, but this does not mean that Portman is necessarily done with the role. Even with her being a non-fan of working with green screen, Portman says that there is still the possibility she could return.
Deadline had the chance to interview Portman due to her most recent role in Jackie, but before the interview was over, she was asked about the chances she would appear in the MCU once more. Portman highlighted her distaste for the current Hollywood trend to use a lot of blue/green screen and the increased requirement that comes with it, but she left the door open for another shot at it saying with a smile, "Yeah, well, hopefully one day I figure it out."
Portman is hardly the first actor involved with big budget films or comic book movies specifically to voice a displeasure with the process that these movies are made. Outside of the Thor films, Portman was involved in the extremely CGI heavy Star Wars prequels, which may be another reason for her not being a fan of this type of film. Even though her comments make it seem as though she could appear again in the future, she may only be saying this because she has another film left on her contract, even though she said she believed her contract had expired.
If this is the case, it still does not seem like she is in line to appear again. The last few times she could have possibly made an appearance, such as in The Avengers and its sequel, the movies have only made quick references to Jane Foster and her current whereabouts. With Thor potentially moving to galactic adventures going forward, there could simply not be a place for Jane in the future. Then again, Marvel could just be holding on to the final appearance to use in the future. After all, Avengers: Infinity War will have no shortage of characters, so Jane could be one of them.