So, let's start with the caveats. This is a rumor, and it's coming from the folks at Schmoes Know, who in the last little while have been okay with their track record concerning this kind of stuff. That said, this could still totally be off base and wrong, but it's intriguing enough to consider.
According to the site, Jessica Chastain is being sought for a starring role in "Mission: Impossible 5" with Tom Cruise, and has received an offer. It's not known what the role would be, but it wouldn't be the first time these two have tried to work together. You might have forgotten but Chastain was originally attached to "Oblivion," but scheduling forced her drop out, and she was replaced by Olga Kurylenko. And theoretically, Chastain would be able to fit this movie into her schedule. Though she just signed up for Andrew Dominik's "Blonde," that movie (last we heard anyway, which was a while back) is aiming to shoot in August. As for "Mission: Impossible 5," it does have a Christmas Day 2015 release date locked down, so presumably it will be rolling before the year is out.
A lot of things need to happen before this rumor parses out (if it's true) including contracts, and scheduling and all that sort of thing. But, considering 'Ghost Protocol' was the most success entry in the series worldwide to date, director Christopher McQuarrie shouldn't have too hard a time lining up big talent for the next adventure, no matter who it is.