I'll depart from my usual legal analysis and put on my pragmatist's hat.  Remember that FinCEN is concerned with detecting, preventing and punishing money laundering.  That is something that they have stated publicly in the past, and it is precisely what they told us when we went to visit them in person in Washington. 

Seriously, let that sink in for a moment.

Because they are concerned with money laundering, their primary concern is the tools of money laundering.  As such, if something is not even arguably an efficient tool for money laundering, then they aren't especially concerned with it.  Airline miles aren't a very efficient tool for money laundering.  They might be a nice use for dirty money, but so is a fancy car.

One of the points we try to emphasize in Washington and with other government officials is that Bitcoin is a terrible tool for money laundering.  That was borne out by the Liberty Reserve.  The last thing money launderers want is a public blockchain telegraphing their efforts to the world at large.  So, instead of using Bitcoin, a decentralized convertible digital currency, they flocked to Liberty Reserve Dollars, a centralized convertible digital currency.  There is still, to this day, no evidence of any major money laundering activity using Bitcoin.

I think it's a strong argument.  It needs to get made more often.