If Ethereum breaks $100 prior to Casper then when Casper proof of stake comes online there is no telling how much higher it can go. The incentives will be to hold rather than sell when you can get interest for doing so. On top of that, there are all these ICOs, and with no mining, there will be lots lf value held in smart contracts. The only thing missing is the Stablecoin or "Steem Dollar" equivalent so there is no reason to cash out to fiat. A stablecoin will close the loop on the economy.