We haven't discussed it yet and since it hasn't been released I don't know how significant the changes are, but I would hazard a guess that we will treat it like we did Doomsday. Release on good version of CORE for the previous game and then move on to the latest expansion with a straight conversion and then a full expansion (to take advantage of new content). Hopefully it'll be "compatible enough" immediately so there aren't any crashes, but we'll see.
But that's just my personal thought on the matter - as I said, the team hasn't discussed it yet.