Well in FFXI when servers got too quiet/their player populations declined enough consistantly over a long period of time they closed the servers down and moved their remaining populations into another server (this happened to my original FFXI server Midgardsormr - it was amalgamated into Quetzalcoatl back in 2010, where my character has been ever since).

1.0 did this too when the servers were replace towards the end of 1.0's life in preperation for ARR's launch. We haven't seen this happen yet here in ARR though as the player population has been steadly increasting ever since ARR's launch, so they've been regularly adding new ones.

But it's definetely possible servers or even data centres may be shut down if they're found to not be too popular, but that would usually be seen through the wider prism of the game in general being much quieter than it actually is.

As others have said, Materia and Dynamis are brand new and just need time for their populations to stablize - the European servers were the same when they were added.