The reason this works is because the cars move slowly along a narrow space. That reduces the danger to pedestrians, and manages expectations; no one is suddenly jutting out in front of anyone else because it's understood as a shared space.
That happens to be a lot closer to what I've witnessed in many Old World cities, including in Paris earlier this summer.
As far as I know, neither Granary Row nor the street in Paris produced any auto-pedestrian accidents during the time I experienced them. That's even though during my visits both places experienced significant auto-pedestrian interaction much more so in fact than places where we typically see serious accidents.
The Granary Row model won't work on every street in Salt Lake City, but in this one regard, it seems to suggest that some streets can be shared by pedestrians as well as moving vehicles.
The experimental "pop-up" site's results seem to be mixed in other regards. I visited numerous times during the summer; sometimes it was hopping, but other times it was almost abandoned. My guess is that has to do with the apparently very low population density in neighborhood. With few people living there at least compared to some other parts of the city Granary Row had to rely mostly on outsiders like me.
Jim Dalrymple II