With regard to the first issue, I am pretty sure Bitcoin would not be considered "foreign currency" even if it is considered "currency" at all. Arguably, it does constitute "seized cash." However, even if it does, the exception for use as evidence would apply at least until there is no chance of it being used as evidence. If it is not cash, however, it could be treated as the feds treat any other seized commodity, and sold at auction at some indefinite future date, subject to internal rules and regulations of the agency. Even then, of course, it could be subject to the "evidence" rule and kept indefinitely.
The disposition of the DPR case might not resolve the issue, as it may still be "evidence" in other cases. If the feds were actually seeking to maximize the value of their holdings (which they often don't do much to do such as by selling properties often on the cheap at auction), they'd find any excuse to hold onto it as long as possible before liquidating.
There might also be some procedure for anyone whose business through SR was entirely legitimate to make a claim on any seized funds. That, of course, assumes there are any such people who would be willing to expose their identities.
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