I think the main reason why we will not see a 960 is to protect the nimbus of the 911.
The 918 didn't hurt, too far away, but a permanent model above the 911 this will hurt the 911 (the cash cow of Porsche) on the long run.

So they decide to sell this kind of cars under another brand. For the whole group it doesn't matter if Audi/Lambo or Porsche sell this kind of car.

Look at the new 718 Boxster/Cayman they sacrifice this model to protect the 911.
The 718 sell very bad for a new model. Almost all german dealers now exchange 718 quotes to 911 quotes. The 991.2 sell better than ever.

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daily: BMW 430d
for fun: Porsche Boxster GTS