One small point about "persist the raw stuff forever": ...maybe don't? I wouldn't go so far as to call user data a toxic asset, but I'd definitely refer to it

One small point about "persist the raw stuff forever": ...maybe don't? I wouldn't go so far as to call user data a toxic asset, but I'd definitely refer to it in the same breath as "technical debt". Sometimes you have to take on some to get anything done, but you need to recognize that it's a potential liability, as well. Persist it as long as you need it to obtain value from it, but after that, you're just holding on to something you can lose some day in a data breach, or build up enough of that people start to get mistrustful (Facebook, Google, etc.) Data expiration policies should definitely be something you think about and have justification for, even if you do decide that your expiration is "Never".