Well, I guess there is a minor error in your assumptions. You won't reach the high speeds with one chip (currently). Minimum is 2-3 chips so far (as far as I know). So they would always. Even with the nand chip of the xbox ssd, it would be at least 2 chips, with high temperatures on a small area. So a multi-chip design was set from day one. And it should still be cheaper to user 4 slower chips to reach the same bandwidth than 2 high performance chips. Going to 6 chips would than only be another price adjustment (I guess).6 chips vs 1 chip?
They are forever bound to using 6 chips going forward for the entire generation I think. I'm not sure that's in favour of Sony in terms of cost especially as 1TB modules drop in price.
* 6x the surface area for cooling, the 6x amount of power...
* 6x the chance of getting a defective chip... a single one of those modules going defective affects your bandwidth, you'd have to RMA your PS5.
They made a huge move sure, but not sure if it's cheaper or will be for them going forward.
Typically as consoles reduce in cost to manufacture, they increase the amount of storage size. So this poses a slightly different challenge for PS5 than it would any other manufacturer, because Sony needs to increase their storage by 6x chips. Series consoles, for instance, would only need to move up to the next chip size, in this case, Series S can move to 1TB and Series X to 1 2TB when those come down enough in price.
I think there's a lot of discussion where people feel that MS is milking everyone for their $$$ for being proprietary, when many consumer NVMe drives are still not using single 1TB modules. So I'm unsure as to how much is cost for the single chip vs. being proprietary. I think in good time, these chips will become the norm as smart phones etc begin to take them on
Defects in those chips should also be a minor problem as nand-chips are easy to produce (without many errors) and thanks to the even lower clocks (with 6 chips) the risk should be actually minimal.
And so far, I don't think they would need to always use 6 chips. They now support almost any 5.5GB/s SSD so using such a thing in the future should be possible without compatibility issues (once the full update is out).