We’re told that Canon continues active development of an EF 24-70mm f/2.8L IS.
At the time of the EF 24-70mm f/2.8L II development, there were prototypes with IS being tested alongside the non-IS version that was eventually released.
We’re told the previous development of an EF 24-70mm f/2.8L IS raised concerns about weight and size of the lens. Which makes some sense once you consider the target market, which is generally event photographers that have to carry and use the lens for 12 hours or more on some occasions.
This tells us that weight and size will have to be reduced before we see such a lens from Canon.
There is no known announcement date, and we doubt we’d see such a lens in 2017, but it’s good to know that development continues.