Actually, that was one of GL's TRUE original visions for SW. Go read that "Secret History of Star Wars" online book. Somewhere in there is an early quote from Lucas about each film being stand alone, possibly with characters from previous ones, but each would be from a new writer/director team, a la James Bond, with Lucas being the SW equivalent of Ian Flemming.
Which explains why ANH wasn't called "Episode IV: A New Hope" back on 5/25/77.