Some issues I see with DRK. tl;dr at bottom
Assuming the coin anonymity feature stands the test of time, most people are still showing their hand in other ways. Just by posting on this forum for instance. Eventually someone will be brought up on charges by the IRS of tax evasion because the government has a backdoor to everything. They are probably busy setting up a masternode right now. And they will catch some drug dealers as well just like Silk Road, everyone was so sure it was secure because maths.
This is just a dumb comment. When your wealth is PRIVATE, you can spend a bit of it here and there and still COMPLY with the tax laws of the country of your residence!