That remarkable power-to-fuel-economy ratio doesn't come cheap. Neither does making a four-seater handle as well as most two-seat sports caras.

The 911 is a four-seater in name
only. The rear seats are useful only if you lack legs. Porsche did not "make a four-seater handle as well as most two-seat sports cars", they just shoehorned a parcel shelf into the back and called them seats.
There are many, many reasons to adore the 911. It's rear seats are not one of them.
Of course they could, but that will never happen. Porsche will never make a car that outshines, the iconic, 911.
Which is why I suggest they retain the remarkable 911 Turbo and GT3/GT2 variants. Replace the base Carerra/Carerra S with an enhanced Cayman. They could make as much money on a Cayman as they do on a Carerra if it was priced at the same point (likely more, since development costs would likely be lower).
I don't think it will ever happen - 911 fans would mutiny - but it's an interesting thought. Porsche
has tried to replace the 911 (remember the 928? Fantastic machine - better than the 911, in many respects), but fans simply would not have it. And I think that remains the case.
I'd still love to see a Cayman "let of the leash", as it were. In looks I actually almost prefer the Cayman to its bigger brother...