On the other hand, after what Tobi and Kabuto did to Edo Zomies (extreme modifications), better be prepared for an overkill mix. The strongest overall Uchiha (front head) - Madara casting Susanoo, the strongest genjutsu user of the Uchiha (left head) - Shisui casting his genjutsu, the strongest ninjutsu user of the Uchiha(?) (right head) - Izuna (It's a guess ;P, based on the relation between Itachi and Sasuke), and the strongest Shinobi, with life regeneration, ocean size chakra and with his face being on everyones bodies - Hashirama on the back. And finally the final portion, Tobi using his phasing jutsu to enter it and thus becoming complete.
More to the point though, I have been asking myself why would Tobi grow a full sized Body of Hashirama, one that has no consciousness, and then have it merged with the Geddou Mazou. The only rational Answer I came up with was that Tobi wanted the Hashirama body for Madara's Soul, and it's Merged with the Geddou Mazou so that Madara's soul and the Captured Bijous can enter into the body through the Statue.
Well, Hashirama's abilities are the source of Zetsu, as well as the secret behind Tobi's body. The Fake Hashirama is also connected to the Gedo statue. Both Tobi and Madara needed Hashirama's powers to become Rikudou/wield the Rinnegan/handle all the Bijuu. Naruto is at the. Ery least a counter to Hashirama's powers (or at least the Zetsu) for reasons yet to be made clear. I think he'll develop a similar power, but Kishi wanted to showcase Hashirama's powers before moving Naruto to that tier just yet. It's the same reason Madara/Itachi are showcasing the Sharingan/Rinnegan prior to revealing Sasuke's EMS power-up (along with whatever else Sasuke will gain to put him on par with Naruto). The very fact that Hashirama's power/hype is still growing is proof that his heir, Naruto, will be even more incredible.