So the list is:
- 16-35 f/2.8
- 17-35 f/2.8-4
- 16-35 f/2-2.8
A 16-35/2.8 is likely to be similar in cost, weight and issues to the current one. It would also be more expensive than the 16-35/2.8 II if it fixed sharpness/field curvature.
A 17-35/2.8-4 is likely to be similar in weight to the existing lenses and priced somewhere between the 17-40 and 16-35. If it doesn't fix the field curvature problems (which I'm hoping it will due to variable aperture) and corner sharpness then it may as well not exist.
A 16-35/2-2.8 will cost and weight more than the 16-35 but it may fix issues to do with field curvature and corner sharpness. I have trouble seeing filters work easily with this lens.
There are not a lot of instances where I use anything wider than 24mm for landscape but when I do, it is not very often that more than 19mm is required. Having the zoom out to 17mm just means that the image should be better when zoomed in to somewhere between 19 and 21.
So my money and hopes are on the 17-35/2.8-4 as despite its variable aperture, it stands the best chance of ticking everyone's boxes - except those that need/want 14-16mm zoom.