Dan answers that question in his recent interview. Just like Bitcoin, Ethereum now that it is operational, basically has huge issues updating to reach a level EOS or even Tezos has aimed for. Eth can update, but expect such improvements to be marginal.

I never expect ETH to process 10,000 transactions per second on their blockchain. Dan likened them doing that, to replacing the engine of a car while the car was running, and you would have to do that without stopping the engine.

Furthermore, technical difficulty ignored, imagine the political difficulty of upgrading ETH that much? There would be about 5 Ethereum Classics out there operating. Eventually, coin politics suppresses innovation, and this applies to ETH's future.