The 100-400/5-6.3 can be considered a scaled down version of the 150-600/5-6.3 super-zooms. It has the same max apertures, same 4x zoom ratio but with 2/3 of the focal length. Seems a bit slow for a 400mm lens, but it is very compact (only 67mm filter) so would appeal to some users, assuming it is sharp wide open.
14/1.8 would be useful for astro-photography, assuming it is sharp wide open - if not, why bother?