I wonder if the reason for the lack of a server merge is due to how people play and where they spend their time today. Back in the glory days, sure 3k people or more on a server at one time would be fine, you'd be spread out all over the world. But now everyone would be in Port Jeuno, Western Adoulin, Delve, Skirmish, Wildskeeper Reives, high level Battlefields, and Abyssea (lol just kidding, felt like people were doing stuff there for forever).

Can you imagine how overcrowded the few zones that people still go to, if we had a server at full capacity? On the one hand it'd be cool, it'd look like the game was newer. On the other hand, I can't imagine putting everyone and their cousin on the same place on the same server would make it easy for the server.