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.
Bitcoins will be always the number because the prices of other altcoins are all depending on bitcoins and that's the reason why the market is always paralleled on its value but there's a huge chance for bitcoins to be replaced by another cryptocurrency if people will focus on investing on other altcoins.