Later, Darth Vader comes in, he and Obi-Wan fight, and Vader reveals that Obi-Wan was his master. (This way, we know Anakin was starting to become evil, but don't know which of Obi-Wan's students is Vader until ESB.

I always thought Lucas should have done something like that. A new prequels story arc needs the "who is Vader" approach, and don't need an answer until ESB. Maybe even without giving any hint. The main character of the prequel could be Obi-Wan and not Anakin. Obi struggling against the rise of Palapatine.