Major problem here is, the the cost per transistor is almost the same. It doesn't get cheaper like before. So you could shrink your the size of the APU but that might also increase error-rates. With a bit of luck you might still get down the per-console price because the cooling-solution can be smaller, the power supply can be smaller, ... but the development costs for such a shrink ... I don't know whether it is ever worth is if the price of the APU is still the same.
Also it might get a bit tricky to get e.g. the smaller chip connected with the GDDR6 memory as the chip is shrinked it might get to small so they might have to develop a new memory connection for the chip (this also costs).
In the past shrinking the chip was always cheaper. Well expect for the original xbox as nvidia didn't give MS the shrink-advantage over in terms of the per-chip price. But that changed over the last few years. Shrinking will no longer give a cheaper chip. And this is a huge bummer for a console shrink.
Also newer architectures almost never give you more performance per transistor. They instead have more performance per clock with more transistors used to get faster. So newer architecture + same transistor count normally wouldn't work (expect if they did something really wrong with the current transistors ... I don't think so).
But I guess with the current generation we will see a more iterative console-cycle as the main bottleneck (the CPU) is now away and they could build on that.
Do I want to look at arse or worse arse? Neither. 
