Atlanta, Houston, Detroit, Boston, Chicago, D.C., & Philadelphia/New Jersey - or a city nearby - appear to be close to ready to go commercial. Only Sacramento and Los Angeles are announced. This is not a firm deployment plan.
Verizon has been doing trials in eleven cities. They are running fiber and beginning to deploy in literally hundreds of other places. They will make final decisions based on the results in each city, marketing, and politics. They've publically committed to 1,000 base stations by the end of 2018, the largest mmWave deployment in the world. That would likely be enough for 3 to 10 square miles per city, but it will not be evenly distributed.
Millimeter wave performance differs enormously based on terrain, height, foliage, and even traffic. Verizon trials and early deployments are locations with different physical features.
In particular, they are choosing to include several different kinds of suburbs. I do not have information on whether the early deployments will be in the city listed, a suburb, or a smaller city nearby.
Readiness, including staff training, is absolutely required before turning on a city. Beyond that, marketing and politics become important. They will want D.C. as soon as they are confident it will go well, for lobbying clout. Boston area is also likely to be early. Much of their 5G research is there.
Even in the industry, very few believe that Verizon is building the best network in the world. THey've committed $20B to cover about a quarter of the U.S. as rapidly as practical. Redefining 5G to include low and mid-band is confusing many, not just the politicians.
This is the real stuff, millimeter wave designed to deliver a gigabit to most.