Well, what would happen with that type of attack is that ethereum would be "frozen" for 6 months or so until a "Proof of Stake" version of ethereum is ready, wh

Well, what would happen with that type of attack is that ethereum would be "frozen" for 6 months or so until a "Proof of Stake" version of ethereum is ready, which would have more protections against this type of attack (because of "Auditable Byzantine Fault Tolerance") I agree the attack would still be devastating at the moment, if someone has a spare $100 million lying around that they want to throw away.