I'm looking forward to the 16-35 f/2.8 III and/or the 1x-24.
The reasonably high probability of a Canon 12/14-24L in the relatively near future is yet another reason I'll likely put the proceeds of selling my 16-35/2.8 II toward the TS-E 17/4L, rather than getting the 16-35/4L IS.
I forgot how useful it was to have AF in the ultrawide range for a walk-around lens until I swapped the 16-35 f/2.8 II for the f/4 IS. Now, I look for reasons to use it. I use the 24-35mm range on it for about 1/3 of the shots I keep. It may not be as good as the 24-70 II, but it is still excellent and saves on a lot of lens changes and renders in a similarly pleasing way. I'd rather have the f/2.8 over the IS, but for now, I like the 16-35 f/4 IS a lot.
The 12/14-24 will likely not accept screw in filters, but the thing I'd miss most from it is the range up to 35mm for shots with people in them. Given the life stage (young kids), I'm more likely to use a 16-35 than a 12/14-24, although I'd look at the 12/14-24 as a replacement for my 14.