I was just talking to someone who was suspecting the leader of the akatsuki to be the 4th hokage.....and I thought of a more plausible approach to bringing the 4th back into the series rather than via the akatsuki.........

remember when oro tried to summon the 1st, 2nd, and 4th hokages to fight sarutobi, but the 4th never made it?
well, that doesnt mean that oro failed to resurrect the 4th.....for all we know, he could be lying dormant in one of the deep cells of the sound mansion.
I expect orochimaru to unleash the 4th on naruto and co. once he becomes a bigger part of the story.