Since Bitfinex knows all of the attacker's addresses, couldn't they try to convince the top pool's operators to blacklist them? Wouldn't that be one of the "advantages" of ultra centralized mining?
So, lets play this out.
The top pools decide to blacklist the BitFinex theft addresses (BFTA). Let's say the top 5. Looking at bc.info (I know it's not the best place to get info but whatever), the top 5 pools have about 70.6% of the hash rate over the past 4 days. So any blocks created by them will not include transactions from the BFTA.
But wait, there is still @30% of the network to deal with. As soon as they find a block, transactions from the BFTA are included.
Never fear, the top 5 pools aren't finished yet! They ignore blocks from the puny 30% and refuse to build on them. Now we have miners 51% "attacking" the Bitcoin network to blacklist some coins. I'm sure that won't cause any problems.
The thief probably isn't stupid either. He starts including huge miner's fees (multiple bitcoins per transaction) to include his transactions in the block chain. The small pools keep building their chain earning tons of bitcoins from fees (which are melted into the coinbase rewards). The smaller miners start upping their hash power with their new found income!
We now have two viable chains. One with fungibility, one without. Hey, Bitcoin is like Ethereum now! Exchanges list both coins (they love getting those trading fees, don't they)! BTCa and BTCb can be traded against each other. The free market decides which properties are more valuable. Hilarity ensues.
Hey, after this, we can hard fork both forks with bigger blocks and have four chains. BTCa1mb4eva, BTCa8mb, BTCb1mb4eva, BTCb8mb. The more the merrier!
I can't wait for miners to decide to fuck with the network over some contentious issue. I'm sure, as businessmen, they are ready to assume the risk that they will be mining worthless tokens in the hopes of picking the chain that the market prefers! No risk, no reward, amirite?