That would annihilate the 911 Carrera, Carrera S, and hell, even the almighty GT3. That is why it likely will not happen. CAR does not cite an internal source so it simply sounds like they are speculating here.
Additionally, Porsche is developing a new series of boxer four-cylinder engines. Those engines will find their way into the Cayman and Boxster. Does this motor not make more sense for the GT4 Cayman? Especially considering how sensitive 911 owner egos are to the Boxster and Cayman having more power which is why the cars have been artificially detuned for so long in the first place.
If the Cayman GT4 gets a twin turbo 3.8 liter flat-6 the Cayman will become a hell of a performance car and Porscheboost is all for it. It just seems very much out of character for what Porsche has traditionally done with the Cayman and Boxster. We will all find out soon enough!