"What it tries to reduce is the ability of someone unrelated to find it n years later."
What it would actually do is reduce the ability of an unrelated individual without cash in hand to find it n years later. A plugin like this would create several new businesses involving the archiving of images posted to social networking sites. Those images would eventually be available to employers for a small fee.
So you really haven't protected the privacy of users... if anything you've diminished it by creating the illusion of privacy, enticing them to post stuff which they wouldn't have otherwise posted, which will be used against them later if they ever want to have a real job, or go into politics, etc.