I thought for sure it would take until the end of 2018 but it looks like this summer ethereum might pass it up. With the turmoil around BTC potential splitting, it might be very soon. IMO this is healthy, we will always value bitcoin for being the one that started it all, but it's time for a more dynamic and adaptable currency to take the lead.
Bitcoin can be replaced anytime since there are a lot of people who are also investing on altcoins and other cryptocurrency, if there will be a new coin that will become the center of attraction of every investors then we can really say goodbye to bitcoins.