https://theflashpodcast.com/interviews/exclusive-interview-part-1-the-flash-showrunner-eric-wallace-on-how-season-8b-deals-with-armageddon-after-effects/
The Flash Podcast: After seeing the reception “Armageddon” got, if there is a ninth season, what are the chances we may see a graphic novel in this kind of scope again at the start of next season?
Eric Wallace: Yeah, I was obviously very happy that people seemed to respond very favorably to it. And again – knock on whatever imaginary object we should be knocking on – if we are lucky enough to get a season 9, I do have a crazy idea that I would love to do as a nice big kickoff to the season with some guest stars. I don’t want to get my hopes up yet. I, like the rest of you all, are still waiting for a pickup too.
But I know how these things work from a more practical level. If we are lucky enough to get that pickup, then very quickly, I’m going to be asked, “Hey, what’s the story next year?” I can’t wait that long. I need to have a plan in place now, so that’s been my job over the last couple of months or so. I would like to have the people who were on the show before in Armageddon, but there’s also some new folks.
I won’t spoil it, but one of the people I’m actually having conversation with in two weeks is a Supergirl alum who has never been on our show before. And I’m going to try and get that individual – notice I did not use any pronouns – onto our show in some way because I love the character so much. One step at a time.
My first guess is Nia?Nia hasn't appeared on The Flash.Niether has Kelly.Has Brainy?Brainy was in Eleseworlds and Crisis On Infinte Earths but I forget if he specifically was in The Flash episodes of those events.
Any Supergirl character I would be happy to see but I do love the idea of Nicole returning for a guest spot on The Flash.