"The Flash" has come to an end with a four-parter called "A New World" Showrunner Eric Wallace revealed in an interview what there was no time left for, including some crossover ideas. "I actually had a two-year plan around seasons 9 and 10, but the second half of that would have been the 200th episode, which was just too good, so I put it in the series finale and then a little bit of new stuff on top to create a new story"