Based on the Dark History of the Uchiha theory:
The Dark History of Uchiha: The Bloodline of Tengu <SPOILERS WILL GET YOU BANNED> - Naruto Forums
It is to my belief that Madara has somehow found away to be even more powerful than he already is by harvesting his father's, the King of Tengu, full demon powers and now wants to release his father into a worthy container. Madara doesn't actually need 3 people anymore because he has two sets of eyes. Now all he needs to do let Itachi and Sasuke have it out and whomever wins will help him release his father so he can absorb the King of Tengu's power and take over the world.
My other theory is that Madara wants to release his father so that his father may rule. But he wants to keep his body so whomever wins the Itachi vs. Sasuke fight will be tricked into releasing the Tengu only to be possessed by it. It would explain why he is os interested in Sasuke. He probably wants Sasuke to be the container. Otherwise he could have just used Itachi. You agree?