>>713304461XIII-2 and LRFFXIII are cheap, unplanned sequels to recover the costs of the Crystal Tools and FFXIV 1.0
A sequel with a fully explorable Gran Pulse would take 5 or more years and be a high budget game. It's not like it was planned anyway, the original project was just FFXIII and FFVersusXIII, with Agito being a smaller game.
Agito became Type-0 and VersusXIII became XV and was totally stripped from the Fabula Nova mythos.
My headcanon is that both games would act similar to Xenoblade 1 and 2, with the connection being eventually confirmed during the story of Versus, probably even with returning characters or references.