I'd be suprised if a 16-35 2.8 v3 will come at all. As much as i'd love one to, I suspect the next UWA we will see will be something similar to Nikons 14-24 with a fairly non-filterable bulbous element.
I will likely be selling my v2 in favour of the new f4. I dont need the IS at all, but really want the sharper corners. I hardly ever shoot at 2.8, aside from when I do some astro type stuff, but I can likely bump up the iso an extra stop to cover that.