after that supply of 100M Ethereum, and like what the other members has said, the value will start to decrease steadly.
Usage is increasing so more gas is being spent, value is added because of the vialibility of this blockchain. This token will more and more be seen as a secured investment. Investment banks and mainstream funds haven't really entered the crypto market yet. They won't purchase just a few thousand tokens.
yeah, 2018 is singled as a year of institutional investments and there is no doubt that it will be remembered as the year of encouraging developments in ETH domain. $1000 is my the least prediction.