Stopped in this afternoon and was impressed. Another 'hound has compared it to Beirkraft and Blue Apron, and that's sort of what I've been expecting too, but there's no comparison. Unlike those other places, which are really specialty shops (or gourmet gift shops, if you will), Union Market is a real grocery, complete with good-looking produce, a butcher counter (not just packaged meat), and a fresh seafood counter.
I was particularly impressed with the meat, some of which is USDA Prime. In particular, I saw some boneless ribeyes with enough marbling to rival anything at Staubitz (and much better than what you'd find at Great Western or A+S). Several all-natural choices too, although I don't think anything was labeled organic.
All in all, impressive. If the Co-Op isn't scared, it should be.