Quite obvious that the dragons will come from the gate imo. Why would they have to prepare it before they actually saw even one? Too predictable.
Also, I bet that Rogue is being controlled by that shadow Gajeel beat the snot out of during the fight, but since F. Rogue has had even more time to train he will last marginally longer against Natsu. But I dismiss the possibility of Natsu losing entirely; no way that's gonna happen especially since he's pissed after F. Lucy's death.
The real question imo is: who or what is that shadow possessing Rogue? Is it a Zeref product? A dragon spy?
Oh and btw, that shadow seems to be from the future as well, since it remarked that the 'current' Rogue could only do this much against Gajeel.