I still think there was a reason for the Plagueis cancellation we haven't been told about. More than simply "George said put it on the back burner... then he changed his mind and made it the main course." I can't help but think he had something else planned (for TCW? the live action show maybe?) that he was still running through in his head and decided he didn't want Del Rey going full-throttle into Plagueis and Palpatine's backstories. And it might not have been Plagueis who Lucas was concerned about -- it might have been Palpatine.