The attack in Thailand wouldn't have been possible without irresponsible lending by banks in risky real-estate speculations (where have I heard that story before)?
And how about when the Bank of England lost to a speculative attack by George Soros, in which he profited some 1.5b? http://en.wikipedia.org/wiki/Black_Wednesday
What makes you think people are not going to irresponsibly lend GoldCoins?
I guess it doesn't really matter, since no one is going to buy the GoldCoins in the first place. Faith in this escrow mechanism is not going to exist.
It is absolutely true that a central bank cannot keep a fixed exchange rate while also manipulating interest rates in a free market economy. I would never argue against you on that. However, MasterCoin makes no attempt to control interest rates, therefore there is no competing goal to allow a speculative attack.
I think I see the point you are trying to make. When a central bank irresponsibly lends, it makes it easier to conduct the speculative attack by borrowing a huge amount of money and then dumping it on the open market. Removing the irresponsible lending does not take away the incentive to conduct the attack though. In GoldCoin's case, it will be much easier to pull off than on a national currency. In fact, the herd mentality will probably cause a speculative attack by itself without any malicious actor. National currencies still retain value when they abandon the peg, and the general population of national currency holders cannot easily go out and dump their GBP for Euros. GoldCoin will drop to zero if the escrow fund's reserves run out, and holders of GoldCoin can easily convert them, so if even a small dump happens and there is any doubt that the escrow funds reserves cannot buy everyone's GoldCoins, then there will be a mad dash for the exit and the first person to sell will lose the least (or if he borrowed his GoldCoins, the most to gain).
I just thought of another problem with this method too. The GoldCoin price mechanism will not be able to track the market in real time, since it uses the blockchain, and so it will be subject to arbitrage and the stabilizing mechanism will lose money. The escrow fund is going to be manipulated down to zero.
I don't really know why I'm bothering to explain this since it is almost impossible for GoldCoin to get in this scenario in the first place. I'm pretty sure I'm just wasting time, so I will send $20 worth of bitcoin to the first person to post after me if I post in this thread again.