Personally, and I don't know if this is possible; after taking a look at what I've used for landscape shots for the last few years I'd want this:
*throw any ideas of f/2.8 overboard, make this a no compromises slow-shooting style landscape lens, tripod almost required, skimping on speed would probably bring the price down..
*zoom range, nice to have, but not a priority, being able to slightly change framing is ok.
*14 or 16 mm FF equivalent..
mind you I've been shooting landscapes primarily with a Tokina 12-24 f/4
I'd love something that is tuned especially towards being sharp from f/8 and as low as possible.. f/16 yes please... (and yes I suppose diffraction comes into play here with the design of the aperture and which sensor is behind it etc..)
Must take filters well, preferably stacked ones, like a polarizer and an ND filter combined or PL + square grads.., oversized front element/filter threads to avoid killing the corners. non-bulbous front element is a given then I suppose.
Big fat focus ring with lots of throw, AF? not required..
Or going one beyond; what about integrated ND filters; swing into place or drop ins?
My shots on flickr: https://www.flickr.com/photos/trondstromme/
just my two cents..