By my understanding of the law. the "FBI" can not sell them until DPR is convicted, as if he is proved innocent, they may have to give them back (although i think this is VERY unlikely to happen).

I would estimate it will take at least 2 years to put DPR on final trial and get sentencing finalised (or aquittal) and officially have the funds confiscated (as i think they are just "seized" at present, and held.... awaiting further investigation outcome).

2 years is a long time in "BitCoin World" and the price is likely to rise quiet a lot in that time, amongst other developments!
I know the FBI have said they will sell them off, but i think they may reconsider if the price increases and other countries "participate" to a greater scale.
Holding 144,000 BTC could put the US in a very good position financially and in "BitCoin World" and i think the "smart derision" would be for them to hold them.
In this time, i also think they are likely to confiscate more Coins.....

It will be interesting to see what they do with them! And good news if they do keep them (even though this wont be popular with BitCoiners)