Not sure where people get the idea that bitfloor "can't" repay USD account holders.
http://en.wikipedia.org/wiki/Fraudulent_conveyanceA transfer will be fraudulent if made with actual intent to hinder, delay or defraud any creditor. Thus, if a transfer is made with the specific intent to avoid satisfying a specific liability, then actual intent is present. However, when a debtor prefers to pay one creditor instead of another that is not a fraudulent transfer.[1]
Given that both Bitcoin and USD creditors "could" sue bitfloor and considering the relatively likelihood of each lawsuit and the relative likelihood of each being successful, the prudent thing for bitfloor to do would be to repay those creditors who have a high probability of success to preempt the lawsuit and seek plans for long term restitution (if viable) for those who's only recourse would be a totally unproven lawsuit of dubious merit.