Ethereum does not directly control with bitcoin and for the foreseeable future this coin can not replace it. Now, no crypto currency can replace bitcoin until it loses its high level of capitalization, which provides it with a price dominance over the other types of crypto currency. When this happens and happens at all, no one can yet say. Of course, on the whole, I would like to see a market in which each Crypto currency would freely form its own price and would not depend on other currencies.