Porsche had already stated they are not doing a car to celebrate 70th.
4.2 will always be out of the question. It's not even logical. Porsche never had a 4.2 engine and to do one just for a 'special' model at the end of 991 production do not make sense at all. It's simply not economical.
Mid engine, easy to do in a race car, the car is empty inside anyway, and there are no government crash test standards. To do one for the road is a different story, especially for a 'limited run' model. Hyper expensive and not good economically.
End of series models from Porsche had always been a parts bin car, with perhaps a fraction of the parts being bespoke, most of which also doesn't cost much to develop.
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