1. The EF 16-35mm f/2.8 is five years old, I don't see Canon replacing it quickly, especially as - based on photozone's reviews - the similar Nikon lenses aren't excellent either.
2. There was a Canon patent published for a 17-40mm f/2.8-4.0 lens. The 17-40mm f/4 is almost ten years old, and the 24-70mm f/2.8 was updated after ten years, so I wouldn't rule this out.
3. Nikon has a 14-24mm, Sigma released an upgraded 12-24mm, and Canon has nothing in this range. Canon might want to release something in this range.
As for lack of rumors - the 8-15mm f/4 was a surprise. There was a rumor about an ultrawide zoom, about a new f/4 L lens, but no patent or "fisheye zoom coming soon".