Noam Scheiber covers it:
There are currently between 150 and 250 firms in the United States that can claim membership in the club known as Big Law, the group of historically profitable firms that cater to the country’s largest corporations. The overwhelming majority of these still operate according to a business model that assumes, at least implicitly, that clients will insist upon the best legal talent instead of the best bargain for legal talent. That assumption has become rickety. Within the next decade or so, according to one common hypothesis, there will be at most 20 to 25 firms that can operate this way—the firms whose clients have so many billions of dollars riding on their legal work that they can truly spend without limit. The other 200 firms will have to reinvent themselves or disappear.
Yglesias adds that, “while the pace of change obviously seems furious to the people at the center of the storm, the genuinely remarkable thing is how long the Big Law model has lasted—not the fact that it’s fading away.”