Someone mentioned Obi-wan having multiple pupils, and it got my cogs turning.

During Episode II, what if Obi-wan discovers that a clone army was being created. What if he discovers the request was made by someone named "Darth Vader?" Later on there is a battle between Kenobi and someone in a proto-Darth costume (possibly replacing Jango in the night/rain confrontation), and during the fight Darth uses a signature move that only Kenobi or one of his students would know.

Then the lingering question as we go into Episode III is, "which one of Kenobi's students is Darth Vader?" And why would they help create a clone army?

And since the concept of clones is so prominent in Star Wars, I've always wondered why no one has used clones as the solution to the whole "Darth Vader murdered your father" conundrum. You could easily have Anakin/Darth murder a cloned Anakin (Anaakin?) in order to keep his identity as Darth Vader secret from Kenobi and the rest of the gang. Plus it solves any issues of having Anakin and the proto-Vader in different places at the same time.

That brings another great reason to add additional students; the concept of a small "gang." You really felt Luke, Leia, Han, Chewie, etc were a team. The PT sorely misses this type of camaraderie.