[...] fork the blockchain so that the coins are in that address, then convice GHash.io and BTC guild[2] to jump on the fork. Everyone's coins stay the same, except the global bitcoin community fucks the FBI and gives back the bitcoins to their rightful owner. [...]
Ignoring the issues of tampering with evidence in an FBI investigation and instead focusing on the snippet above,
everyone would need to download and use the new blockchain, not just the largest pools. Not to mention an act like this would completely undermine the concept of Bitcoin, making it worthless.