Our migration plan to the latest version of Minecraft is as follows:
1) Wait until 1.9 and its respective Bukkit release is released so that the world generation code is mostly stable.
2) Set the default world into which you'll first enter upon login to a bare survival server--no admin codes at all.
3) If possible, use multiworld to set up portals into the current server (creative survival) and possibly further creative worlds.
The existing creative survival world will remain intact, but be aware that once we do enable access into it post-1.9, traveling into areas that haven't yet been generated may create terrain features that don't mesh well with the existing world. I do think most everyone will stick with the default survival world, however.