Tetsuya Nomura has once again been interviewed by Japanese gaming magazine Dengeki and within the article are some interesting new details concerning all the Fabula Nova Crystallis titles. Here they are summarised.

Nomura is no longer involved in the development of Final Fantasy XIII. All the character design is finished so he's moved onto working with his own projects.
He's currently concentrating on Final Fantasy Versus XIII and Final Fantasy Agito XIII.
The battle system for Agito has evolved since we last saw it.
Even though Agito is on the PSP, they're aiming to make it the pinnacle" of this handheld generation.
Final Fantasy Versus XIII is being developed by many members from the Final Fantasy VII team who are working well together.
The team isn't making any compromises so the quality of the finished product should be great.
They're currently testing the battle system and map gimmicks in Versus.
Versus will have a day and night cycle.
Nomura wants to show the result of leaving a character on their own for a long period of time.
He asks us to be patient for Versus information. Once he gets to a certain point he'll have a surprise for us. (Versus won't be shown at E3 almost 100% confirmed).
Final Fantasy XIII will have new screenshots and a trailer revealed at E3.

Thanks to our forum member Cagalli for finding this.