The only difficult to trace transactions in Bitcoin is from transactions which occur purely in btc and don’t touch anyone with a financial license.

Think drug dealers/gangs recirculating bitcoins mined years ago. Now the tricky part of this is that it would only take knowledge of a few transactions in the networks identity, complete with purpose to start identifying everyone. I’m sure an AG is looking forward to the largest RICO case in history at that point.

I’m sure that folks looking to anonymize are aware of this and take further precautions, I’m also sure that there is someone in the network who is dumb.

If I was in law enforcement I’d make btc address collection a top priority.