In Town & Country's recent profile on Dunst (via ThePlaylist), they say there has been "talk of a third film with Sofia Coppola in 2016". There isn't any more information than that, so let's start speculating. Dunst has the second season of FX's Fargo on the way, and she'll star in Jeff Nicholas' sci-fi film, Midnight Special. Next up for Coppola is her Netflix holiday special with Bill Murray, but the only movie she's signed on for is an adaptation of Alysia Abbott's Fairyland, which she agreed to co-write a couple of years ago. Could that be it? Has Coppola decided to direct it, as well? The film certainly boasts the sensibilities she's known for, centering on a young girl living in San Francisco with her bisexual father, a poet and gay rights activist, during the height of the AIDS epidemic.
Whatever the film turns out to be it's worth paying attention to if it reunites Coppola and Dunst. Assuming the date is accurate more details should be available soon.