It's only been announced (technically), but XV may be ripe for sequels. Queried on the E3 trailer's end text (stating it was the beginning of the VERSUS epic) at a post-presentation Q&A, Square-Enix's Shinji Hashimoto suggested that there was more stories to come from the world.
"More information will come at a later time, but because FFXV is such a large-scale game with so many great stories, many other stories may come at a later time, but details will be explained by the development team at a later date."
Given how side-sequels are now a normal part of the Final Fantasy franchise, with FFXIII closing as trilogy come Lightning Returns release, its shouldn't be surprising that the company could continue the idea for FFXV.