7nm would still be more costly then than 14/16nm is right now. If a PS4 Superslim would come out this year then most probably not below 249$
More costly ? Nah, at least not by much so it's only a tad more expensive per transistor ...
Even if cost scaling had stopped, there's still many savings to be found aside from the chip itself such as using smaller boards, moving to passive cooling, smaller case design and using a smaller power supply unit ...
Best of all there's GDDR6 for the masses! Sony can redesign the APU's memory controller so that they can deliver 2x higher bandwidth/density per pin for even more savings ...
Who said anything about scaling? It seems you didn't get the point.
It's just way too early yet to move to 7nm. Your link is from mid 2016, when the 14/16nm processes where already very well established. But for the 7nm process, we are at a point like mid 2014 was for 14/16nm processes: Too expensive yet for mass production, but tech is getting tested with some early designs of future chips.
For reference, your article is from June 2016, almost a full year after Apple came with the A9 in the iPhone 6S/S Plus or Qualcomm with the Snapdragon 820, and over a full year after the Exynos 7420, all having been produced in 16/14nm processes, meaning the process was already ripe at their releases. What he's saying in the article is anybody who hasn't made the jump yet will be left behind because there's no reason anymore to produce high performance chips in 20/22 or even 28nm to avoid bad yield rates (and thus high prices) anymore.
Oh, and Sony isn't designing anything, they are just asking the chip manufacturers if they can produce a chip which is able to do what they ask (and pay) for. So if it can be done cheaper with GDDR5, they will take it no questions asked.