Final Fantasy XIII may be seeing an official sequel, if a new domain is any indication. Siliconera reports that the domain name "Finalfantasy13-2game.com" has been registered, fueling rumors that we'll see the continued story of Lightning and her friends.
The domain registration itself would be unremarkable if not for the associated name: Corporation Service Company. It's been used for the registration of other domains for Square, like the original Final Fantasy XIII which is registered under the similar domain, "Finalfantasy13game.com."
Square-Enix poured years into the Final Fantasy XIII, and the associated costs couldn't have been cheap. Bringing it to the Xbox 360 was one way to help recoup the investment, and since the engine is already built a sequel would be significantly cheaper to make. Square has also been eager to build games around the world introduced by FF13, but efforts like Final Fantasy Versus XIII have been plagued by delays. An official sequel would add one more game to the Fabula Nova Crystallis stable.