Materia DC and DC travel.
Disclaimer:
I don't play on Materia anymore, i left because it was a horrible experience with how small the player base is. People have other opinions, and they have every right to have them. This is my personal feelings on the DC and nobody elses.
Main:
Materia Datacenter suffers from the lack of accessibility to a player base large enough to sustain itself. Queues can be hours long for content such as Alliance Raids and off-peak regular dungeons.
Some people are fine with this, but others are certainly not, and end up leaving.
I personally moved to Dynamis DC, another fresh DC that has access to DC travel, alleviating all the problems that Materia DC suffers from by simply having access to larger Datacenters to travel and play on.
Materia DC NEEDS access to Datacenter travel in 6.3, Majority of the players from Materia are originally from Elemental, there is no reason why Materia is not linked to JP servers, other than the Language Difference (Which shouldn't really matter because Majority of people played there for years anyway).
If JP is out of the question, Give Materia players access to DC travel to North America.
Every day i see more and more OCE players moving back to Elemental or NA. Square Enix need to address the issue soon, as it's becoming more and more of a ghost town as time goes on.
DC Travel has to be implemented in order for the Datacenter to function normally.