Earlier today Disney announced via the DisneyParks Blog that the Rivers of Light show at Disney’s Animal Kingdom will be delayed. They did not give a new date except to say they will update everyone in mid-late May. So that is pointing to a summer premiere at the earliest. No real indication was given for the delay.
As part of the announcement they included the video below showing the new lighting and projection on the Tree of Life that will be part of the expanded evening offerings.