Now that Healing Tide will be a baseline spell for all Shamans in 5.4, Blizzard needed to replace the tale previously occupied by Healing Tide. They have announced a brand new talent called Rushing Streams.
This talent will increase the healing done by healing stream totem by 100% and cause the totem to heal to targets at once. It will share the same talent tier as Ancestral Guidance and the newly redesigned Conductivity.
Because of this change, I expect that many resto shamans will be considering keeping their T15 tier bonus and take advantage of this talent. However, because of this, I expect we could very likely see the T15 bonus nurfed by Blizzard shortly after T16 comes out and the new tier is available to resto shamans.