We've heard some chatter that Canon would continue to develop it's non-L zoom lenses for full frame camera lineup and this patent for an EF 17-35mm f/4-5.6 IS would seem to fit into that segment.
Canon News, a new leader in patent tracking found this one.
Canon EF 17-35mm f/4-5.6 IS STM Optical Formula
- Focal distance: 17.50 25.12 34.09
- F number: 4.00 4.85 5.88
- A half field angle (degree): 51.03 40.73 32.40
- Image height: 21.64 21.64 21.64
- Whole length of the lens: 130.88 128.52 134.05
- BF: 37.60 49.75 64.06
Japan patent application 2017-161568