darth_ender said:

Somehow there would need to be allusions throughout the film that Palpatine may even have a backup apprentice, just in case.

A great reason to remove the "Always 2 there are" line.......I hated that they limited themselves that way. Would have been much cooler if Vader, while not only wiping out the Jedi, also had to wipe out the Sith they happened to be fighting, or just other random Sith in different parts of the galaxy. Imagine a Jedi VS Sith lightsaber battle going on, and all of a sudden Vader shows up to carry out order 66. You'd have feeble alliances between Jedi & Sith while trying to defeat Vader.....then turning on eachother again when opportunity is sensed.....and of course Vader ultimately wins the day. Scenes of Vader killing other less powerful Sith in an effort to be the only one left (an early start on balancing the force)...etc etc....