Is it confirmed that there won't be IS? Or has IS simply gone unmentioned so far?
There's no CR3 on IS to my knowledge.
People tend to lump the 16-35 f/2.8 and 24-70 f/2.8 lenses into the same 'workhorse handheld zoom' bucket, and it appears that in that bucket, Canon would tend to go [f/2.8 non-IS] or [f/4 IS] for such lenses. My money is on non-IS for that reason, but Canon may shake things up and offer it for the video crowd.
So who is the bookie that takes all these bets you make?
If there was a bookie for this, I'd fear for my financial future.
It's also being called the 16-35 f/2.8L III according to CR, not
the 16-35 f/2.8L IS.
More circumstantial evidence to the 'non IS' camp, I guess.