No. We are not planing to replace Neptune anytime soon.
we might look in replacing Neptune come 1.9 or 1.10
In every update; we look at the changes and check if overall what would be the benfits/Cautions if we were to bring a generated new world at that version
At this point of time Survival will not be replacing Neptune to a new world at 1.8, mainly because there isn't too many new natural biomes
Some of the other servers (excluding survival) might be replaced but we will give you notice and how it effects everyone.