Players who purchase the digital update right now won't receive the actual content until the next version update, which is tentatively scheduled for early April. So it's more of an announcement of a pre-order being made available soon... on a digital product.
Hey, we're not marketing and business guys or anything, but isn't that kind of silly? We see no need to pre-order something that has an unlimited amount of "copies" and exists in an ethereal, digital, online state. Maybe if Square Enix offered some kind of little bonus for pre-ordering, that'd be one thing. As it is now, we guess this affords someone an ethereal, digital online piece of mind.