Maybe I've misinterpreted the situation - I don't own a Vita, though I might down the line - so forgive me if I'm off-base, but I'm having a hard time coming to terms with how there's blame being directed towards the victimized customers here.
Why should anyone presume that Sony would lock them out of their personal data for simply updating the official firmware? If the "one memory card, one account" policy was truly obvious from the start, then why did the Vita ever give users the option to format their memory card when switching account regions? Why would it let them choose not to format it? I simply don't understand how that could be a "loophole" in any real sense of the word. If Sony originally intended for users to have one and only one account per memory card, then what point could there possibly have been to allow data from multiple accounts on the same card?
Bearing that in mind, the problem is not that Sony closed some ambiguous loophole that allowed users to circumvent the Vita's intended functionality - the problem is that Sony removed an existing feature without warning: the choice to format one's memory card when switching account regions. That, in turn, locked paying customers out of their personal data without their approval. If that's not a bait-and-switch, then what is? It's not like you had to crawl through eldritch, non-euclidean labyrinths to take advantage of this feature, either.
If the writing was truly on the wall in the first place, it sure wasn't written clearly - at least from an outsider's perspective. And that ain't cool.