I can see it opening up in 4.2 at the earliest and later. They already opened Gilgamesh up and unless they lock it back up, it's population will grow just as big and they'd have no reason now to unlock Balmung.

When they first announced these locks, it just seemed like a way for them to soften the expansion hype causing server instability and double bonus of mitigating the amount of people rushing for houses later down the line. Just a tad bit more patience really. They'll open it in a few patches, if not the next one.