Going by tradition there will be one of 3 possibilities in order of probability from most to least likely:
1) Expansion only, with the base game getting a nice hefty discount on PSN, Steam, etc. leading up to the release.
2) Expansion only with a separate option for a "bundle"
3) Expansion+base game together.

My money is on #1, which is the most common MO for expansion for MMOs.