Really good article Dave and something we've spoken about in depth a lot over the last few years.
Something worthwhile pointing out on the cost front, PCIe storage is the cheaper option compared to a SAN if doing a new build (where you have to factor in the SAN cost). I've just recently looked at the costs for a new SAN setup with 1.2TB as the basic requirement of storage capacity. On the SAN side I've gone for 4x600GB disks (RAID 10) and a dozen servers. I've looked at dedicated spindles per DB server as always (I would have preferred 300GB disks but it's the better balance for the example I was working on). The SAN is a Clarion VNX5.
For PCIe I went with the FusionIO ioDrive2 Mono MLC card as an OEM bit of kit shipped from Dell. The rest of the server spec is identical to the above. It's more than fast enough but there are much faster.
The cost of PCIe is well under half the SAN based costs and will deliver a lot more performance (I upped the RAM spec on both sides as I found the requirements as you mentioned from FusionIO and it's not that more expensive to allow at this stage).
On the lifespan front you can use the program / erase cycles to calculate the theoretical lifespan.
The lowest number you normally see quoted is 10,000 p/e cycles. Using that value we can calculate (simplified theoretical version) :
A 1.2TB drive = 1,318,554,959,872 bytes
1,318,554,959,872 bytes * 10,000 p/e cycles = 13,185,549,598,720,000 bytes that can be written
500GB written per day = 536,870,912,000 bytes (for me this is pretty close as TempDB takes a hammering in our estate)
1,318,554,959,872 bytes / 536,870,912,000 bytes = 24,560 days of writing at 500GB per day
24,560 = 67 years or 589,440 hours (admittedly lower than half of SATA or SAS, but when you up the capacity to 2.4TB with the same write rate it almost matches the usual MTBF rates on mechanical storage [my preferred way of describing SAN storage without being offensive]).
It's a bit of an unfair calculation if I'm honest as we are comparing the amount of times we can theoretically write to something vs a potential hardware failure rate with mechanical parts. However, since the end result is something being kaput it's probably not too wide of the mark. Adding more component parts increases the probability of failure so that is something else to consider with mechanical storage. If we add spindles for speed we increase the likelihood of something breaking.
Oh and once you see a 1TB database restore go from 4 hours to 5 minutes simply with none-mechanical storage it's very hard to get it out of your head.