Which service will tumble 32 million worth of coins? And if they do them per bust then people will still see a transaction of x amount leaving their wallet.
Exactly, regardless if they tumble it, they still have to tumble it. Which creates plenty of technical and legal challenges. I personally doubt they would essentially launder their own seized money for future operations.
They aren't going to tumble all 32 million. Even 10k-20k USD worth of coins is enough to work with for most criminal cases.