IMHO, one year ago, Josh Jones (CEO and Founder Bitcoin Builder, Inc.) trusted MtGox would recover somehow and accepted buying GoxBTC with real BTC at a price, thus offering a way out of Gox for the (desperate?) people. Of course that would make no sense if GoxBTC was to completely evaporate. Some, like me for a few BTC, also bet that way.
The simple thing to me now is Josh again thinks GoxBTC can somehow recover from the present zero. From inside information or just as another bet, he must be trying that again.
I would not be so optimistic as to think 200K/800K = 0.25 BTC per GoxBTC (for there will be a lot of money spent with lawyers, experts, theft, etc.), but that s a number, why not. On the other hand, with current BTC value, maybe a lot more can come out. I would not exclude 100% recovering of BTCs @ the present 200-250 USD range.
For Josh, when BTC was around 1000 USD, GoxBTC went down to around 100 USD, so 0.1 rate. Now, at 0.1 BTC per GoxBTX it is again 0.1, what makes 1 cent of original BTC per GoxBTC, what is not bad.

And of course Bitcoin Builder got trade commissions as well at that time.
Finally, about withdrawal etc, for what I know about Bitcoin Builder, I bet yes, it is probably instant cash for those wanting to sell BitcoinBuilder-GoxBTCs. Just a feeling, but I trust them.