Even though it's a little taboo to mention, the truth is: Bitcoin's developer abandoned the project years ago and disappeared into thin air. If he was still around he would be actively evolving the coin and addressing issues like this one in a clever manner. Bitcoin without Satoshi is like Apple without Jobs.

To my understanding, the only coin actively developing a 51% defense is Goldcoin whose developer is actively building upon Satoshi's unfinished work.