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.
Its totally fair to acknowledge the steady growth Ethereum has made during its course but I still don't think it has the power to overtake Bitcoin. Perhaps in the fututre, who knows what will happen...