It's those dang VmWare guys
Diversity in networked storage solutions was always a function of workload diversity. But with virtualization reaching 100%, the Hypervisor is the only client that midmarket storage vendors need to design for these days. Of course there are still differing performance profiles for different guest workloads, but the point is that the host environment (networking, provisioning, protocols...) has gotten much simpler. So these 3 things represent the bulk of all cannibalization of the legacy array market:
1) Practical adoption costs for using public cloud are much reasonable once you're virtualized
2) Startups can optimize strictly for the virtualized use-case (thus creating differentiation)
3) The hypervisors can handily disintermediate the value chain (EVO-Rail!) and put everyone else out of business (or force them into OEM servitude)
So what's left for the storage vendors? Probably just the vertical workloads (Web2, M&E, HCLS, GIS, analytics, PACS, etc etc).