Serious question: what sensitive user data is there on Stack Overflow anyway? Questions, answers and comments are all public, the content is Creative Commons licensed and even available in handy downloadable & queryable form: https://data.stackexchange.com/ As far as I can see, the primary sensitive user data they have is e-mail addresses, but (unlike, say, Reddit) most StackExchange forums don't deal with personally…
I've seen plenty of questions that include API keys or credentials and they're later edited to "remove" them although the revision history is still there. It would make up a minority of content on Stack Overflow but it's still there.
https://meta.stackexchange.com/questions/2677/database-schem...