How would a user mix their NXT coins so they cannot be linked to previous accounts that sent it to the user? One way I thought up of was to deposit your NXT coins into an exchange and take it back out into another account. This is assuming that exchange has alot of transactions to blur the transactions.
The coin shuffling feature is on the product roadmap but I don't know when it will make to the mainnet: https://bitbucket.org/JeanLucPicard/nxt/issue/135/coin-shuffling-monetary-system