Final Fantasy XIII will be an odd beast, containing a primary entry (currently an exclusive for the PS3) and several spin-off titles, a la Final Fantasy VII; the collection as a whole will be entitled Fabula Nova Crystallis. However, only two spin-offs had been announced: Final Fantasy XIII Versus, also for the PS3, and Final Fantasy XIII Agito, available for mobile phones. These were apparently the only planned titles until the above (beside?) picture surfaced, clearly showing at least three more unknown entries in the series.
Square-Enix knows how unbelievably profitable the DS is, and recently released review scores of FFXII: Revenant Wings will ensure solid sales in Japan. Personally, we find it hard to believe that one of these titles won't be coming to the DS, and heck, who knows ... there might even be a Wii title in there too.