I think you're reaching the wrong conclusion here. There is absolutely no need for the next generation to be on 7nm. At least not to be 4 times as powerful. Changes in architecture can have some profound effects on performance.
Best example is Nvidia's Maxwell. The 980 on 398mm² packs more punch than the 780ti on 550mm². Both are produced on 28nm.
In case of an APU we also have to consider that the room for the GPU will get disproportionally bigger than the room for CPU on the die. So 2x the size for both will mean more than 2x the room for the GPU.
Next thing is the form factor of the console itself. With more advanced cooling solutions and maybe a bigger sized console they will be able to sustain a higher clock and pushing the performance even more.
4x the power on 14nm compared to 28nm is absolutely feasible given appropriate advances in architecture and design of the console.
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