First of all, I don’t think any other movie that I can remember has ever been this bookended before as will Star Wars Episode 3. We all know what happened before, and what will happen after.
I have seen discussion of E3 in a number of different threads, but i’m interested here in what has to happen, not what might be a nice plot thread.
Here’s what I’ve come up with so far (in no order, since that would be indicating I know more about the plot than I do):
[ul]
[li]obiwan gets anakin’s lightsaber for luke[/li][li]obi-wan hides kids[/li][li]leia get adopted by bail organa[/li][li]luke get adopted by owen and beru lars[/li][li]yoda to dagoba[/li][li]anakin gets nearly killed by obi-wan, rebuilt[/li][li]vader kills jedis[/li][li]anakin goes to dark side[/li][li]no more jar-jar[/li][li]no more dooku[/li][li]empire established[/li][li]no more amidala[/ul] [/li]
I also think it is very likely the connection between Palpatine and Darth Sidious will be revealed, but I’m not sure.
It would also be fun to see some future characters introduced on some level - Jabba, Han, Chewie, Lando, etc, but that’s not critical to the plot.
Any other ideas?