Assuming he will have something new to show us (shame on Kishi if he doesn't), I think it's interesting Kishi decided to save his feats for last, in respect to the four hokage.
Gotta save the best for last.
Orochimaru fought on a jounin's level against him. He didn't used anything special besides the Edo Tensei.
Hiruzen, despite his old age, showed NO FATIGUE despite doing all A rank techniques and he wasn't doing anything special either against Orochimaru. Hiruzen wasn't serious that entire battle, he didn't want to fight his masters, yet held his own against three kage level opponents.
We told and told and told people that he would come BACK!!! and they never believed us. The fools! All Hail Lord Third. He actually made Hashirama's wood style seem like nothing.
That's true, Hiruzen fans, including me, have said time and time again that Hiruzen would return, but no one listened. Hiruzen has shown yet again that Hashirama's Mokuton is nothing to him and we might finally get a chance to see Hiruzen's real power.