Yes, that's right: Facebook is opening up the option for subscriptions to its games in the hopes of drawing in more money. Subscriptions are already being tested in several games, such as KIXEYE's Backyard Monsters. This coincides with the development team's shift away from Facebook Credits as a universal microtransaction currency for all of the many games floating around, mostly since developers preferred to use in-brand virtual currencies instead.
None of this is particularly new to MMO veterans. It's still rather interesting after years of business model changes to see subscriptions being touted as the future of payments.
[Thanks to Space Cobra for the tip!]