while Guennael and Peter are absolutely right about the adoption of Big Data in consulting services, I believe your question was also aimed at the question whether Big Data will actually disrupt the industry itself.
And I belive that there certainly is a possiblity for that. You have seen it with the advent of information readily available online, that the pure "knowledge advantage" of consultants has shrunk. A large corporate will have access to any database that a consulting firm has access to - and often more.
I believe that the same thing can happen with big data - companies that adopt a highly analytic, data driven approach will be able to extract a lot of insights that they previously needed consultants for by themselves. but of course, some will need help in getting to that point - and then we are talking about consulting again.
The question is whether the "classic" consulting forms will be able to adopt quickly enough to offer really data-centric insights, or whether this will go to a new breed of advisors.