Thinking mainly aboit landscape on tripod I don't need much aperture or even IS. Just wondering, under which use cases would you need f2.8 wide angles? Events/weddings?
Opening up the aperture doesn't just reduce the depth of field - it also yields faster shutter speeds for the same ISO. So if we take the depth of field at ultrawide angles as being minimally reduced by shooting at f2.8 instead of f4, it's for anyone who wants a fast shutter speed, or keep the same shutter speed with a lower ISO. Which means any photographer shooting moving subjects who want to minimise noise. Events, weddings, sports, and stars all spring to mind.
As useful as IS is, at such short focal lengths camera shake only really has an effect with a very slow shutter - so this is purely of an advantage to photographs of completely stationary subjects, and of course videographers.
I photograph both still and moving subjects with an ultrawide, and due to the usability of long shutters without IS, I believe a brighter aperture is of more use than IS for me with this mixed usage. Therefore as I'm in no pressing need to hit the buy button right now, I'm going to sit this one out and wait to see what comes of an f2.8 ultrawide zoom. And I can rest assured that if nothing comes up before I need to jump, there'll be a damn good f4 IS option available as a backup plan.