File this one under the long list of issues addressed several years too late, if ever.
According to Matsui direct from
Freshly Picked Vana'diel #17:
Q: Are there plans to merge servers due to the declining player base?
A: At least until the completion of “Rhapsodies of Vana’diel” in November 2015, there are no plans for merging unless something major comes up. After completion,
we do have some plans in the event that players are giving feedback about not being able to form parties and more players voicing their requests for server merges. As far as how we’ll merge, we’ll be looking into how to handle this such as merging two Worlds into one World, or transferring players from one World to a World of their choosing.
Such a small percentage of players take the time to come here to the forums, unfortunately. I did my part to direct those unhappy with the pitifully low population numbers to make their voices heard, but they chose to stay silent, so I wound up making the move from Cerberus to Asura with a couple of close friends not too long ago and wish I had done it sooner.