I saw the Versus XIII logo, went "Whaaaat?!" Then it changed to "Final Fantasy XV" and I nearly fell out of my chair. Amazing. I called this months ago (as did many others), and I think it makes the most sense for Square Enix. It's a bit sloppy, and they made a bunch of mistakes this gen, but I think this is a good way to salvage things.
Their decision to rename Agito XIII was one of the first signs they were scrapping the Fabula Nova Crystallis saga. FFXIII and its sequels seem to have replaced that. By "upgrading" Versus XIII to FFXV, they have an excuse to devote more resources to it and they can get away from the bad associations that some fans have with FFXIII.
I'm all for this. I hope the game's great. This may force my hand on getting a PS4 far earlier than I usually get new consoles depending on when it comes out.
I believed in you, Square. I still do!