Ethereum won't surprass Bitcoin because it is worse when it comes to scaling. Currently, the whole transaction history of Ethereum is way bigger than Bitcoin's which causes a lot of problems. People don't synchronize their nodes fully which means that Ethereum network might become less secure over time. Bitcoin will continue to be number one thanks to Lightning Network.
It is expected that in the coming months ethereum will implement the Plasma project, which will allow this coin to have scalability of hundreds of thousands of transactions per second instead of the current fifteen, then the possibilities and popularity of it will increase even more.
As for bitcoin, someday it can be overthrown from a leader position. However, this can not be in the near future, first bitcoin should lose its high level of capitalization.