the similarities b/w revenge of the sith and return of the jedi are EXACTLY the reason i think it is a possible title. we dont need to see how Episode II ends, because we already know. We also know essentially what the plot of Episode III must be.
Look at the similarities so far:
A New Hope/The Phantom Menace. Both simple, three word titles to start of the trilogies. Neither Title really reveals too much about the plot, but are titles that merely set the tone for the upcoming movies. Phantom Menace is negative, b/c the mood of the upcoming trilogy is negative. A New hope is positive, because in general, the series ends very positively.
The Empire Strikes Back/Attack of the Clones. Both 4-word titles. Both Titles denote specific actions, and in simple terms, describe a grand conflict. They also both carry the idea of a real, and verifiable threat.
Return of the Jedi/??????? Ok, i will first start off by saying that Return of the Jedi was rumored to be originally titled REVENGE of the jedi. But for obvious reasons, it changed to return. We also have the term Jedi in the title. What better way to contrast the two films, which wrap up their separate trilogies. And in order for EPIV/A New Hope to be a sensible title, EPIII, must have a very negative one. Revenge contrasts Return. Sith contrasts Jedi. I promise you, in one way or another Sith WILL be in the title for episode III. The whole trilogy is about them.