We've received another mention of an EF 16-35mm f/2.8L III. We're told the announcement for the lens could come at any time, as the lens is “done”.
We have no firm announcement date, as that is always a difficult thing to nail down with lenses. With the arrival of the EOS-1D X Mark II, it makes sense that a new L lens would follow relatively quickly.
We do not expect to see it for the CP+ show at the end of this month.