Went back and read his blog, late last year he said earliest would be fall 2016 but plan for 2017 so you're right. If there is any author that I think could actually meet a stretch date it would be Sanderson though, so still hoping.
Here's his schedule:
January 2016: Wax and Wayne 3
February 2016: Reckoners 3 (final book)
June 2016: Alcatraz 5
Sometime 2017: Stormlight 3
Sometime 2017: Rithmatist 2
Spring 2018: New YA project 1
Fall 2018: Wax and Wayne 4 (final book)
Sometime 2019: Stormlight 4
Sometime 2019: New YA project 2
Sometime 2020: Elantris 2
Sometime 2020 New YA project 3 (final book)
Sometime 2021: Stormlight 5 (ending of first arc)
Sometime 2022: Elantris 3 (final book)