When will the Volcker Rule be in effect?

The earliest is July 21, 2015, five years after Dodd-Frank passed. eight years after the Great Recession began. But it may be later than that per this part of the rule: “The Board will continue to monitor developments to determine whether additional extensions of the conformance period are in the public interest, consistent with the statute.” Why the need for an extension since Wall Street has known for over three years that it has to divest itself of activities banned by the Volcker Rule? Why do they need another 18 months or longer?