IOPS are now a commodity item.
One thing that specifically changed to make large dual-controller SAN's less interesting is that random IOPS are now essentially a commodity item. In the Pre-SSD era, the only way to provide thousands of random IOPS to a host was to lash hundreds of spinning disks together. This was a) expensive and b) hard to do - requiring dedicated hardware and software. A modern Intel DC class SSD (e.g S3700) can provide up to 70K random read IOPS. You would need around 350 SAS drives (assuming 200 IOPS per drive) to generate the same IOP capacity.
As a result we no longer need specialized hardware to drive high IOP rates.
Full Disclosure: I work for Nutanix, previously at NetApp.