Same thing happened with the offering of GLD in 2005 (http://finance.yahoo.com/q/bc?s=GLD&t=my&l=on&z=l&q=l&c=). There was huge demand to buy gold easily. And, outside of buying gold futures, it was nearly impossible to get 100% exposure to the gold market. So GLD came along and at it's max in 2011, the thing held $80 billion worth of gold. Just about every investor on Wall Street wanted to diversify into it. GLD, however, was/is only a market risk diversification tool / value-storing tool. It doesn't have the actual usefulness that Bitcoin and crypto-currencies do. In other words, you cannot buy a pizza for gold like you can with cryptocurrencies. Hence, I think a Bitcoin ETF will be huger than GLD was at it's peak.
Tying this back to Darkcoin... immediately after the Bitcoin ETF's likely successful launch, every major Wall Street bank is going to want to create their own products around Bitcoin and other crypto's. The GLD ETF launch immediately saw the launch of dozens of other gold-related, silver-related and metals-related ETF's.
Sorry for side-tracking, but just a note: I understand the easy nature of GLD however large investors and funds are shooting themselves on the foot with it. They'd rather buy a few tons off a refinery and take delivery. It's counter to their investment to allow the gold possession by ETF.
It's like masternodes. You get the 1000 DRKs and pull it OFF THE MARKET so that price goes up. If you bought the 1000 and these 1000 remained 100% liquid the effect would not be the same.
With ETF this gold is not really taken off the market so the investor is going against himself. The investor wants to take physical delivery and increase gold shortages that make leveraging paper-to-physical and overselling physical that doesn't exist => less possible.
It's like what Keiser did... buy silver, crash JPM. But take delivery in the process That's how the price goes up.