Ultimately these coins are gone. Since more coins have been mined since then, any work to evict the transaction from the blockchain would do more damage to miners.

Imagine this were 500000 BTC and every MtGox user were at risk of a major loss. (which would certainly hit the news and damage the community).

A feature that allowed a miner to vote out a block or a transaction would be valuable. If 50%+ did it, the error would simply vanish. Democracy at work. But it would only work if that 50% voted immediately.