=== Disclaimer, Im not a Storage Vendor Employee, but i do own several vendors equipment === ;-)
Now i think most people can agree on that Distruptive Upgrades are a unwanted risk to a platform in general. And to me it would be close to unacceptable, even though im not running a "Enterprise Senario" (we only have 1200 employees, in EMC talk that would be SMB).
Im not exactly sure why a disruptive upgrade would be needed, but from what ive read it has something to do with changes to the Metadata in the array. I am not sure why it cant handle more than one metadata type, and just do internal migration of the data to a new Set but im sure there are technical reasons as to why its not possible. EMC should look into that, and implement it so future updates would not require them to be in the same situation. That ofcause depends on their architecture beeing in a state that allows for this.
If i were an EMC Customer, i would assume that my Storage Partner or EMC directly would provide me with some sort of Migration Path in form of either a physical array, so the data could be replicated, and the unit either be replaced or upgraded without downtime on my Production enviroment. I assume that is what EMC means by their press release/statement. If not, that is clearly unacceptable. Relying on downtime and/or risk of dataloss incase of inadiquate backup is not in any form acceptable. Even in VDI solutions.
My newest Storage Array (a 3Par 7200), will be getting inline deduplication soon (flash only unfortunaely), and i doubt HP would allow the upgrade to be disruptive. It simply isnt "Enterprise", to do so.