If Star Wars was originally to be three trilogies, which no matter how many times he denies it is the truth, then the series should have ended with what we know as the OT. THOSE should have been episodes 7, 8, and 9. The first trilogy could have established the Republic in its waning years, the grandeur and history of the Jedi and their relationship to and conflict with the Sith. Obi-wan could have been the focal character for this particular set of movies. The final film of the first trilogy could have dealt with the introduction of Anakin and the beginnings of his realtionship with Obi-wan.
The second trilogy would have dealt with Anakin's maturation and quest for greater power as a Jedi that ultimately leads him away from the order. The seduction could have been stretched over the three movies, as well as the rift between Anakin and Kenobi. Sort of set up the first cracks in the foundation at the end of the first film, and then develop them into the full fledged split by the end of the second film, which could see Anakin's wife fleeing into hiding with Obi-wan at her side. The third film would focus on the culmination of Anakin's turn, the beginning of the annihilation of the Jedi order, and Obi-wan's hunting of Anakin that leads to the big duel. Each film in this trilogy would have to be at least two and a half to three hours to do it right.
If there were to be three trilogies, I think something along these lines would have worked best.