We’re hearing more about a new EF 16-35 f/2.8L III, which is expected in 2016 along with one of Canon’s new “pro” body announcements. We’re not sure if it’ll arrive around the time of the EOS-1D X replacement in early 2016 or the EOS 5D Mark III replacement later in the year.
We’re told the new lens will be slightly longer and a bit heavier, and will retain the 82mm filter thread diameter of the current lens. Weather sealing, durability and optics will get obvious improvements. The lens hood will also be unique to the new lens, but we weren’t told what “unique” meant.
There is little to no chance of IS making its way into the lens. You can get the EF 16-35 f/4L IS if you want stabilization.
You can see the latest patent for the optical formula here, I think we’ll probably see another one before the announcement.