It's a known fact that a rear engined car is not the good solution.
Nonetheless, Porsche's engineers have managed to make the 911 one of the best sports cars in the world.
I think that a rear engine is one of the essences of the 911 along with the Flat6.
So I personally think that the next 911 will be rear engined with a flat6 and no mid engined version.
The latter could be a super Boxster or a mini Carrera GT if you prefer, let's call it Boxster GT
Fanch.