I have the feeling that Orochimaru is going to take Sasuke to one if his unknown hideouts and perform an Edo Tensei on the First and Second, this is why I believe this:
In part one Orochimaru summons the two Hokage to fight the Third, but the point of this is to show that he has access to their DNA. He apparently is the only person to possess Nidaime's DNA and one of the few who can summon Shodaime.
It has been stated that they were in an alliance with Madara, who else would have intel on him? No one else faced him and survived save OOnoki and the two Hokage.
The Second was rumored to have kept a close watch on the Uchiha, how close is debatable but it begs the question, what secrets did he uncover?
If my assumptions are right (and forgive my arrogant tone but they usually are 9/10 times) then the best two, those two whom Orochimaru speaks of could very well be the First and Second Hokages, the only other intimate party to the nature of Madara was Izuna and I think it highly unlikely that we'll see him.
So what do you think? Could it be possible that "those two" are actually the first two Hokage's?