So what profit motive do you have to buy GC at 50% backing over just owning MC?
The motive would be because you want to own GoldCoins, and you believe the escrow fund is still healthy enough to maintain their values. Maybe that will be too risky for some people. For me, 50% does seem dangerously low, but not necessarily destined to crash. I think I'd be just fine with 75% though.
Hopefully I'll have a lot better idea of what level is safe once we create a few unsustainable ones "just to watch them die".
*why* do I want to own gold coins except for immediate payment to someone else? In the short term volatility of BTC doesn't matter and thus short-term ownership of GC doesn't count. Why would I want to hold them long-term when they have 100% or less backing?
If you believed the escrow fund was healthy enough to sustain GoldCoin values for the time you would hold GoldCoins, and you were interested in owning something which tracked the value of gold, then this would totally make sense.
Again, I really don't know if 50% is enough or not.
Who eats the losses from the volatility and how are they compensated for their risk?
GoldCoin volatility is absorbed by arbitrage traders at first, and ultimately by the escrow fund. The cost of volatility is borne by people who buy or sell GoldCoins at prices which are off-target. The premium they pay for their off-target transactions goes straight into the escrow fund, making it stronger.
If I own gold coins back by 50% escrow... my risk is the same as owning MC because there is no reason for GC to be worth more than 50% escrow because to make such a bet is the same as betting the MC will double in value. Thus, no profit for buying GC when I can just own MC until GC has 150% backing at which point I can see owning GC.
I suggest you rethink the market dynamics on how you will make a profit for the fund because it is not possible for you to increase the backing of the fund except by appreciation of MC vs GC.
Saying that traders would take the losses is like claiming that BTC traders absorb the cost of volatility. I have already shown that GC will be just as volatile as MC when escrow is less than 100%. You have not shown me how GC escrow fund grows back toward 100% absent any change in the value of MC.