To wit, Willisch told F30Post.com that a V6 was under consideration for quite some time, and the original thought was to use a chopped version of the S65 4.0-liter V8 found in the current car. But plans for a V-configuration have indeed been ruled out, and all that's left to speculate on is exactly how much help the new inline-six will get from forced induction.
In order to be more powerful than the current M3, no less than two turbochargers will likely be bolted to the new six-cylinder powerplant. In fact, we've even heard rumors of a tri-turbo setup being engineered for use in the M3. In any case, expect about 450 horsepower to be on tap.