How will he know I validate ETH-new's chain? I can spend on both chains, and I'm sure he would be fine by the assumption that I'm selling the ETH-new he disapproves of, to buy his ETH-old. But, you can't know with certainty that an ETH-old staker uses the same funds to stake ETH-new. Say, for example, that I mixed ETH-new, and then staked those.