What about demand?! It is about to burst out!
You are only looking at supply. Demand is about to undergo a huge shift. AI in its many flavors, AR, VR, and, perhaps especially for NAND, autonomous vehicles ("servers on wheels") will be demanding huge amounts of NAND and DRAM. Timing of course is critical: will autonomous vehicles be ready for prime time by 2020 or 2021? Some certainly say yes, especially taxi and delivery type vehicles. If so, they will soak up a enormous supply and that supply needs to be there if autonomous vehicles are to be built in volume. So, it becomes a chicken-and-egg issue. The storage and memory vendors don't want to wait until everything else is finished. Everyone is moving ahead on all fronts. Worst case scenario is that the memory and storage vendors leave some clean room space vacant for a few months to a couple of years while other problems are resolved.
The vendors have, for the most part, said that they will decide how to use the clean room space that they are building after it is built. Intel is the exception to this; Dalian will be used for their 3D NAND. WDC just said in their CC that they will talk to Toshiba about what to do with the fab they are building. And both Hynix and Samsung have said similar things in recent weeks about their new capacity. Micron is expanding clean room space, but they are not adding many new wafers. People who comment on expanded clean room space appear to ignore the fact that it takes more physical space and equipment to produce the same number of wafers of NAND and DRAM at current geometries. And the truth is: none of the established vendors wants to create a bust. They have been there, done that, it is counterproductive. They have become adept in recent years at bringing up their fabs slowly, so that they don't overwhelm the market. And of course they do want to increase the proportion of SSDs in PCs and laptops as well as servers over the next few years. The price is gradually becoming compelling. I know my own desktop 7200 HD is becoming increasingly annoying when compared to my speedy laptop SSD. For a hundred bucks and a few hours, I can remedy that.
If there were still a dozen or more NAND and DRAM vendors, then perhaps you (Chris) would have a better point. But there aren't. And while there are some new entrants from China, IMHO people are making an error if they believe that those new fabs will be producing large amounts of either 3D NAND or DRAM soon. The vendors with decades of experience behind them are having production difficulties at the current tiny nanometer sizes.
That's my two cents for now.