This might be a little bit of my hope talking but don't go all. "that can't happen!" I'm not a fortune teller. This is just me thinking of ideas. We have some rumors going of a spin-off from Supergirl starring Superman. This is a likely idea when the DC extended universe bombs heavily and the TV world can use more characters. Oliver and Barry will be more experienced heroes and practically on the same level as Superman by the time they form an orginazation that defends the earth from threats much worse than Vandal Savage or the Legion of Doom. They finally form the Jusice League! Kara goes with Rip and his team because she has always been associated with time travel. Jonn Jon'zz also joins but much more than Kara due to her having her own show. Catlin becomes Killer Frost and joins the Injustice Gang with many other villians like Lex Luthor, Grodd, and the Acolyte. Deathstroke will also guest star on the team. This is when things get a little less likely. Wonder Woman and Green Lantern will get shows based on them. These two heroes will be a part of the Justice League along with Green Arrow, Flash, Superman, Hawkman, and Hawkgirl. Batman will crossover with the Justice League from Gotham by the time he is an experienced hero. However he is a loner and will not be with them often. Other guest starring members of the Justice League will be Atom, Vibe, Supergirl, Mr Terrific, Firestorm, and Vixen. There are also going to have younger heroes crossing over for one episode of a show. These young heroes will be Miss Martian, Kid Flash, Artemis, and Superboy. In the regular adventures for the Flash and Arrow world. Barry will be stuck in jail because of the death of his nemesis the Reverse Flash. Without the Flash, Barry's friends have to deal with the new problem that is Grodd's invasion on Central City. Cisco comes out as a hero and other Flashes like Jay and Wally help as well. Meanwhile, Joe and the rest of the team try to get Barry out of jail. This is when Catlin starts to get colder and colder. Nobody can figure out why. After they defeat Grodd with Barry out of jail to save the day, Catlin starts to leach speed off of Barry but it's helping her not freeze to death. As later in the season, team Flash deals with this by containing her in a heating cell. Catlin only finds this is a temporary measure and won't solve the problem. That is why she joins the Injustice Gang, even though she hates them. (except for Grodd) It's the only way to find a cure. To leach Barry's speed. On the Arrow side of things, Oliver fights baddies like the Calculator, Malcolm, Slade, and Prometheus. Oliver continues training new heroes like Artemis, Wild dog, and Mr terrific. He also is getting older and grows a goatee. In the world of Supergirl, Kara has to defend the earth from Cyborg Superman. She discovers that he is really Hank Henshaw. (The real one) This is an emotional battle for Kara, who has to battle someone with his cousin's face and the brain of the man who killed her adopted father. Batwoman also arrives in National city after billionare Kate Kane is inspired by Supergirl's actions of saving National City. She meets Science Police officer Maggie Sawyer, and forms a relationship with her during her brief guest starring appearances. The Legends deal with many different threats in the DC universe, but none as powerful as the Anti-moniter. With the help of the Justice League and the Teen Titans, they weaken the Anti-moniter. He tries to gain in power by travelling through time and absorbing greater power from other earths where they meet Jonn Jon'zz. In the end though, the Legends save the day and call themselves the new Justice Society.
I hope you enjoyed this list, please be nice about it in the comments. This is just my opinion and i would like to hear yours.