Well, Porsche felt the benefits simply outweighed any negatives and completely revised their PDK transmission for the GT3. One essentially still has full control as if they had a traditional manual and can disengage the clutch at any time. Very, very trick and very cool of Porsche to do this.
Additionally, Andreas goes into why the car ditches the GT1 block that the racing GT3 still uses. His reasoning is that since the Carrera and Carrera S DFI engines dominate the production line they simply had to make this switch partially out of space requirements. It seems to be a move out of convenience and to keep costs down as well.
The motor does share some parts with the Carrera S but it has titanium rods, a new forged crank, forged pistons, and a whole new cylinder head which clearly is very efficient. And yes, the GT3 now has direct fuel injection. The race cars have not made this jump it will be interesting to see if they ever will.
And what about the Nurburgring laptime for the new car? Well, it apparently matches the GT3 RS 4.0 so that means sub 7:30. Expect something around 7:27 which is incredibly fast and actually better than Porsche hit with the Carrera GT.
The interview is below, well worth watching.