There's always going to be the possibility of money laundering as long as there is any medium of exchange that can't be tracked. Even btc through coin mixers could possibly be tracked. Although it would take considerable time and money to do so since it would require following a lot of dead ends. They'd have to then use something like Shadowcash, it says it's 100% untraceable. Then convert it back to bitcoin to convert to cash.
The problem is never going to be solved. As long as there is something to protect people there will be a way to exploit it for bad. Encryption, Weapons, etc.
I also think that individuals that don't have an outside identity will be in the position to earn the kind of money needed to launder a large amount of funds. Most high earners will have a verifiable identity. If they don't users will question and ask for verification, etc. These type of users wouldn't want the attention. That in itself is a form of prevention.