The Restatement of Law Governing Lawyers was "conceived" in 1985, as the Foreward to the bound volumes tells us, and completed in 1998. The books have a 2000 copyright.
Since 1998, the ABA Model Rules have been significantly amended at least five times and there has been much new caselaw. We have also seen the growth of non-traditional providers of legal advice and services, including from persons without a law license or organizations that are not traditional law firms.And we have the Sarbannes-Oxley and Dodd-Frank whistleblower provisions.
Granted that the Restatement like the Rules should ordinarily lag behind societal changes, some of which flame out. But too much of a lag risks making them less helpful or entirely unhelpful. This certainly happened when, in 1977, the Kutak Commission was formed to revamp the old Code, less than eight years after it was adopted. Its shortcomings had become apparent even earlier.
Also,while there is much to be said for a lag, there is also much to be said for leading.
So: If the idea of a new Restatement were "conceived" -- by whoever does the conceiving -- in 2014, we might see a final product by 2021 because the second time around can build on what we now have. That will be 23 years after the ALI approved the current Restatement.
I don't know how often other Restatements get revised. Maybe 23 years is too short. But surely it also depends on events in the world around us. And for the law governing lawyers, there have certainly been events in the world around us.