Re: "whether the technology to build/operate FABs more cheaply is evolving too?"
"" the continued efforts to finally deliver the promised "Extreme UV" AKA Soft X-Ray lithography."
Are not required for Flash.
Features smaller than 20nm are a liability in NAND, resulting in slower cells with lower endurance and significantly degraded cold-storage performance thanks to electron migration. There are strong arguments to stay at 40nm for the same reasons.
That's why 3D and chipstacking became the standard methods. The problems with parallax are well-defined and surmountable. Neither technology will significantly benefit from EUV litho.
In fact, most NAND production is done on old dry DUV tools. No need for immersion litho on NAND structures and the dry machines generally have a more robust uptime. I know of atleast one semicon fab using equipment produced in the early 2000s for NAND production.
The biggest hurdle slowing down NAND production uptick is simply available manufacturing for dry litho systems. Not many companies produce litho tools to begin with (only 3 players basically, Nikon, Canon and ASML. Of which ASML is the biggest due to better throughput performance per tool) I doubt all of them together manage more than maybe 500 tools a year in this segment.
If you really want to increase production 10 fold you need 10 times the machines already out there in the field. If there is a 1000 tools now (probably an underestimate) that means you need 10.000 systems. At current production levels it would take 20 years to meet that demand.
And that's just litho tools. The same constraints exist on all of the other equipment needed in a semicon fab. It's also not the kind of business where you can decide to increase production 10 fold in a year. I know for the tools I work on some of the critical supply chain path runs over 10 levels deep. Several of which are monopoly suppliers which won't like having to jump trough hoops just to get a small customer (for their business) some extra parts each month.