NAND life span
NAND Flash will clearly not have the same life span as magnetic disk has had so far (40+ years) but it will serve its purpose over the next 5-7 years. The cost per IOPS compared to magnetic disk is so much more favorable and the demand for more IOPS will continue, there's no doubt about that.
I suspect PCM & MRAM and perhaps HAMR have about that time to grow to maturity. The interesting point is, as Chris mentions in the article, will that mean that current NAND Flash based solutions will have outlived their usefulness and therefor make for a unattractive investment vehicle?
I'd like to think that having a several year head start in building purpose built high throughput systems will allow them to adapt. Several of the CTO's of All Flash arrays I've spoken to are already brainstorming on how to incorporate PCM/MRAM as a replacement for NAND flash.
Until there is a replacement, NAND flash is what we have to work with. And I suspect that period will be five years at least, but lacking a crystal ball, time will be the judge.