Obviously Disney can just keep making spinoffs forever, and we know another trilogy of some sort is in the works, but what do you expect will be the last numbered episode?
After IX though I think theyll rest episode numbered films for a minute. Do the spinoff films and the Rian Johnson trilogy. See how those do and if they dont deliver money wise go back to numbered episodes.
I also think after IX that will end the trilogy set up. Theyll just use episode numbers and have storylines last as long or short as they desire