Here is a scholarly article on Canadian legal malpractice trends from the Practice Pro blog site.  Its conclusion is that wills & estates legal malpractice cases are on the rise, and will continue this trend. 

Risk managers look to frequency and severity in their analysis of trends.  Frequency is the raw number of cases.  Severity is the potential dollar amount of the losses.  As estates [and the wills that create them] benefit from the prior years of real estate and stock appreciation, claims concerning malpractice in their handling will rise in severity, simply as a matter of inflation and appreciation.

Beyond that, the frequency is also rising.  Historically, education on the issues of legal malpractice in a specific area and publicity of successful cases contributes to this trend.