TS-E 17mm. period.
And 400 DO II. I'd miss that too.
Plus if you don't like Canon DR, you can always get a used Sony for landscapes and use the Canon lenses. Actually that might be my next camera. Why get a 5DIV for the extra DR and MP, when I'd need that for landscapes on a tripod using LV anyway. Might as well get an A7rII or III.