>without a planned ending

That's true of all Star Wars trilogies, though. The norm in Hollywood is not plan ahead: if you plan, you get "locked" into a certain direction with the plot and the characters that you can't necessarily get out of, if audiences don't like that direction.

The classic Star Wars trilogy was like that: hence out-of-left-field nonesense like Leia being Luke's sister. But even the prequel trilogy was like that: it was only planned insofar as Lucas knew "Yoda and Obi Wan must survive and go into exile, Anakin must turn into Darth Vader, Palpatine and the Stormtroopers take over."