Being long time Archviz artist, I’ve found that Atmospheric Fog in UE4 can work pretty well as a replacement for Physical Sky model often found in offline render engines. It unfortunately suffers from two severe flaws:
1, Screen space reflections do not work correctly with it, as they need some background geometry to establish depth. This can be partially worked around by introducing giant skybox sphere around your scene, but it often interferes with the Atmospheric Fog look.
2, Sun disc drawn on the Atmospheric Fog has completely wrong intensity. I’ve reported the bug here: Unreal Engine Issues and Bug Tracker (UE-58668) and answer is “Won’t Fix”… go figure. So at this time, despite Atmospheric Fog being a better Sky model for Archviz than Preetham or Hosek/Wilkie, it’s bugginess and refusal of Epic to address these issues makes it unusable and UE4 will likely require yet another Physical Sky model on top of the existing one instead.
By the way, if the intent of the efforts is to make life easier for archviz people, then I would suggest implementing some 1-click algorithm, which would find HDR spots on the HDRI map (above defined intensity threshold), compute their radiance in proportion to the given scale, and automatically create Directional Light(s) with appropriate direction, intensity, color and source angle. That would save so much time.