bitcoin will always maintain market domination, first because its still the most liquid crypto ever, that can easily be converted to other currencies, so there will always be demand for bitcoin hence its dominance will continue based on this simple fact.
Bitcoin will always remain the top dog, but we shouldn't ignore the fact that Ethereum will keep growing as well. I don't like Ethereum, but we just have to admit that regardless of its purpose, it does very well.
On the other hand, if after all the years only Ethereum managed to grow this large, then it shows how weak this industry actually is. It will be extremely difficult for any coin to come close to Ethereum.
In an instant it wiped out the need for another platform to launch ICOs and other stuff on. What other than Ethereum does the market needs? It can do everything other tokens can do and it has the crypto mass on board.