I don’t see how this is a design for cost reduction - rather it’s a reduced cost (for what it offers) design from the start. Not one heck of a lot you can do to reduce cost now other than wait for the components themselves to get cheaper due to improvements in manufacturing. It will happen, but not at the pace of yore. It’s not a given that, say, a shift to 5nm lithography in 2023 would reduce costs by a lot. NAND will slowly get cheaper over time but it may well be that Sony will simply leverage this to improve their margins a bit.
It may well be that by the time process technology has evolved to a point which used to motivate a mid-life redesign, it’s time for a new system entirely. We’ll see how Sony chooses to play this, but there is nothing I’m aware of on the horizon that would reduce either cost or power draw (allowing a new enclosure) by a major factor. What would that be?
Did PS4 ever get a die shrink? I would think at this point the cost of doing a shrink is so big that it's not worth it.