We think they are waiting to see how many people return to the game after the final RoV, how many people are staying in FFXI to build the new Aeonic Weapons, and other long-term challenges.

The current Trust-infused game is tailored towards lower server numbers, and if a huge number of people return to FFXI, this may cause some problems. Will people still solo Dawn with their trusts, while the rest of the server waits outside? These are the type of things to be considered, is my guess. I'm only guessing, and also I think server merges would be fun. But it seems like they are going to review the population numbers next year, and try to manage any merges so that it doesn't negatively impact gameplay.