Zooms.... Are not primes.
I'm not a big fan of very-wides, myself, but when I use them, it's usually either something very prosaic, or I'm trying to do art and don't want disappointment. A little, high-quality one's just the kind of wide that'd be there with me once in a while when I need it. This one's really of interest to me, actually, though, it'd be way down on any priority list, anyway. For where I want to work with a zoom, if Pentax made a 28-85 2.8 as well as the 16-50, and offered me the choice, I'd be all over the former.