I'd like to see how Madara spent all his years, when no one thought he was still living...
Minato's life would be interesting, how he advanced in his ranks, trained, etc...
I'd love to see Itachi's point of view of the Naruto Universe...
Hm... I would personally like to see a series of Madara and maybe Izuna and see how they grew up like the full story and maybe side events. Maybe that will show us who Madara fought and how he fought when he awakened his MS with Izuna and took over the clan.