Latest word on the grape vine is that apparently Bartz uses everyone's weapon's in Exmode, whilst summons are also available, and activated by using Triangle+R.
I've yet to find artical, or scan, so its all rumor as far as I'm concerned. But it definetly sounds interesting. Chupon and Ifrit were mentioned, though from the sound, they merely apear as stat boosters, apearing as flashing images of their amano representations, as opposed to being fully 3D attacking versions of themselves.
Sounds a bit of a let down.
Still a few more things left to speculate and hope for over the next two months.
1. Mascot apearances
2. Terra/Cloud/Kefka/Sephiroth/Exdeath/Golbez's gameplay style
3. Further explaination of Summons
4. Supporting character possible apearances
5. Monster apearances.