Gawd Awful Expensive, at first, perhaps a long time.
Chris you keep bringing up the point about the flash manufacturers are at a hard wall in the amount of flash they can crank out. Now, if you are stacking about bunch of them together, exactly how are you going to meet demand? Sure, using a more relaxed geometry should improve yield but the number of dies that are produced is relatively fixed.
I get it. "Spinning rust" is dead, except for the fact that we've found a way to produce less flash product packages. The next two years, perhaps three, will give us more information about options similar to flash (XPoint, PCM, ...). But until you can put lots of packages in the sweaty hands of system builders/integrators, I'm reserving judgement. Oh, and I have two 150 GB and one 600 GB enterprise 2.5" drives which are extremely wonderful so long as streaming in a serial data set (or media file if that's your thing) and then back out at the end of the run. Otherwise, it's wall to wall flash in six packs.
[I suppose being one of the last to learn how to operate a card-sorter, remote job entry station, and gawd help me paper-tape to boot the computer, might have to do with the fact I still find ISAM useful in certain cases.]