Brandon Sanderson has issued his annual "State of the Sanderson", confirming what projects he will be working on in the coming year. On the Stormlight Reddit community, he has also issued a larger-scaled overview of his Cosmere mega-sequence and where he sees the series going.
For 2017, Sanderson will be releasing Oathbringer, the third Stormlight Archive novel, in November. The Lost Metal, the final Wax and Wayne novel set on the Mistborn world, will likely be released in 2018, alongside his next YA novel, The Apocalypse Guard. The second White Sand graphic novel will also likely appear in the next two years.
For the Cosmere overall, Sanderson envisages the story now encompassing the following series:
Elantris: A three-book series. Elantris itself was released in 2005 as Sanderson's first novel. Elantris II is on the horizon and getting closer, but is not imminent.
Mistborn: Originally a trilogy of trilogies, but expanded to 13 volumes with the addition of the Wax and Wayne sub-series. The first trilogy is done and Wax and Wayne will be done by the end of 2018. There will be two further trilogies. The first will be written in the gap between Stormlight Books 5 and 6, with the final set of three books acting as a capstone to the entire Cosmere mega-series.
Warbreaker: At least a duology. Warbreaker itself was released in 2009 but the sequel, Nightblood, which will bridge the first book and Stormlight Archive, is a long way off.
The Stormlight Archive: A 10-book series, unfolding in two five-volume halves. Books 1 and 2 are out and Book 3 will be out at the end of 2017.
White Sand: Originally planned as a trilogy, but now being released as a graphic novel trilogy instead, with Book 1 already out.
Dragonsteel: A planned 7-volume series which will explore the backstory of Hoid and the 17th Shard, the glue which holds the entire Cosmere together. However, Sanderson has indicated this series may be shrunk to 5 volumes and possibly just an ultra-focused trilogy. This will be the second-to-late Cosmere series, with only the last Mistborn trilogy to follow on from it.
Sanderson has also confirmed that he still plans to write and release Aether of Night and The Silence Divine (although one or both may be shrunk down to novellas), as well as a novel set on Threnody (the planet of the Shadows for Silence in the Forest of Hell novella) and possibly a novel sit in Silverlight (a city mentioned in Arcanum Unbounded, possibly a city-between-dimensions where worldhoppers can hang out, like Sigil from Planescape).
This puts the total Cosmere series at around 36 novels and three graphic novels.