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.
As of now there are hundreds of hundreds of bitcoin that have been discovered and there are still hundreds of hundreds coins that have not been discovered so I think someday for sure one coin will stand out and bitcoin will be replaced by other cryptocurrency, but for now let us celebrate that bitcoin is still on top.