This seems insane. Shouldn't it be cheaper and more efficient to just sell them on an exchange or something? (Over time, even, rather than all at once, obviously.) "Let's sell them all in blocks of 3000 and require a deposit of $200k to bid" ... yeah ...
If you were the US Marshals, would you entrust the government's money[1] to an unregulated Bitcoin exchange? [1] As to whether the government is morally, ethically, or legally entitled to the seized properties, I have no opinion. I don't know anything about the situation.
These coins were technically owned by all the people with accounts on the Silk Road and were not necessarily going to be used for illegal transactions. For all we know this is basically government stolen money from some guy who wanted to buy a sandwich with Bitcoin just for the laughs and to say he did.