I'm having trouble forming an opinion on it.
On one hand the GT3 is supposed to be the ultimate machine from Porsche, transmission technology is a big showcase for technological advancements and also shave seconds off lap times and acceleration, effectively making the car look even more competitive on paper.
On the other hand, the GT3 is the kind of car I probably wouldn't drive daily and I would definetaly find it pleasurable having a manual on such a car ripping through country roads. I'm pretty confident that Porsche knows it's clients well, and most people who buy GT3's track them and probably would enjoy having the latest and greatest from Porsche, even if it means no manual.
The real answer, is that I wouldn't buy a GT3 so I don't really care. If I was in the market for a Porsche it would be a 4S or Turbo with the PDK transmission and I would drive them year round in Montreal.