One of the use cases for external storage is clustering in its various guises. Just about any HA solution relies on external storage as a shared resource. Then there's VMware's Vmotion and the features that depend on it, like DRS. Fast internal storage will work for many use cases but what you allude to for EMC in the future in the form of an appliance is what most mid-range storage arrays are today: a pair of "servers" running magic sauce managing access and availability to data on a bunch of disk drives. IT breaks, good idea not to have it all in one box. Slightly less radical: faster, and maybe cheaper, interconnects could be what's needed. Did Paris say FCoE?