Lucas briefly toyed with the idea of a 12-episode saga. Episode I would’ve been the prelude to the Clone Wars trilogy, with Episode V serving as an interquel between the Clone & Star Wars trilogies. That would’ve given us 4-5 films in which to explore Vader’s rise and fall.
What could’ve been. But this is why I’m partial to rewrites/fanedits which jettison the episode numbers altogether.
Where would episode 6 have gone then?
Episode VI would’ve been the film we already got in '77.
Anyway, here’re Lucas’ handwritten notes for the proposed 12-episode saga:
Couldn’t find larger copies, so you’ll have to squint. Sorry.