Given satisfactory performance from the final product, I'd be interested in a 16-50 f/4L IS, as well.
I bought a 17-40 right after they came out 10 years ago; I was shooting with a crop-sensor body then, and the 17-40 became my walk-around lens. When I moved to full-frame, my new walk-around became the 24-105.
I'm very happy with my 17-40, but don't use it very much anymore, due to its limited zoom range. I think a 16-50L with current IS and all the other recent tech would be a nice upgrade, and something I would use more often.
In the meantime, I wait (not so) patiently for an update to the 100-400, and -- much longer term -- a 24-70/2.8 with IS (unless my 7½-year-old, heavily used 24-105 dies in the meantime).