The populations for Balmung / Mateus / other worlds are server based and not datacenter based. Moving servers to another datacenter on its own will not change the point in which servers are locked.

What might help is the world visit feature. If players on high population worlds change servers within the same datacenter in an attempt to do something like acquire housing, the world visit feature would still let them travel to other worlds on the datacenter while being able to switch to a lower population home server.

In the end, the locks are server specific and require fewer players on that server to loosen.