ok my idea is this
The key to Madara/Tobi's plan all along was the fight with the first hokage and it was never about defeating him, it was a diversion to get his DNA which he used to create zetsu/tobi/rinnegan. Tobi is a special zetsu clone or just a host for madaras will. How Tobi can have Madaras will while still being able to be summoned by edo tensai is the main problem with this theory but that will get explained kishi style. Sasuke and Nagato are huge parts of his plan as they were both meant to groom the ultimate eye techniques for madara/tobi to later steal and use himself. He needs to EMS and the rinnegan to become the jyuubi jinchuriki like the sage was. Madara knew he wouldnt be able to gain the power of the first hokage with out dying so he set up his revival as tobi.
something like that, gg crash
edit: sorry to those that didnt want the story spoiled, blame crash