For a long time, for many tech companies, the idea of getting a listing, especially on Nasdaq, was one of their highest goals. In the past few years, though, more companies are choosing to stay private or delay their listings.

Meanwhile, Nasdaq is implementing a big change in the form of blockchain—a system that underpins the digital currency bitcoin and allows companies to make and verify transactions on a network instantaneously without a central authority. For a look at what these changes might mean, The Wall Street...