The 911 is both an iconic and aspirational car to many. It will continue to sell in sufficient numbers for Porsche to continue justifying the cost to develop and build new variants. For every owner who has had several examples and become bored of the rinse/repeat design formula there will always be new customers to the brand or those moving on from either the Boxster/Cayman or, more as is more likely the case now, moving up from a Macan or Cayenne. As Wonderbar points out from his personal experience customers have been getting "bored" of the car for decades and dropping out of ownership and trying other marques out so it is nothing new to feel as a customer that you require something new and different. It is easy to forget that this is still a low volume model in real terms so glacial change for such an iconic model is really the only way for Porsche to maintain it's allure to future customers. How many manufacturers wish they had an evergreen model like the 911 in their range to provide a real sense of connection with their history yet always be the top of it's segment for performance. I would wager Audi wish they had continued with the original Quattro model and gently evolved it as their brand halo car. Such a model would have had greater relevance to their wider range than the R8 has.

A new interpretation of the 928 might appeal to repeat 911 buyers looking for something fresh and have wider market appeal with a 2 + 2 layout than a mid engined 960 and likely generate higher margins as a result.