It's not data limitations, it's not server limitations. It's not even limitations. It's been said already, the only reason Square would merge servers is to reduce costs by merging the lowest population servers. The only reason to reduce costs is if the game is on it's way out. We're only a couple months into first expansion with the second expansion already being worked on, we're far from 'on it's way out'. I foresee server merges happening in a few years, but that's a few years from now.