Because of season 5 of Arrow ending with a big bang, what's going to happen now? I have some ideas.
A New Villain: During the previous seasons, there were villains who were rich and successful such as Malcolm Merlyn, Slade Wilson, Ra's Al Ghul, Damian Dhark, and Adrian Chase. So why not introduce a villain who has known of those qualities? I was thinking that maybe Stanley Dover AKA The Star City Slayer. Since Stephen Amell no longer wants any magic, I was thinking they could make the Star City Slayer similar to the Trinity Killer from Dexter. Dover has a wife, son, and daughter. He abuses his family while pretending to be kind to them in the public eye. It would be interesting to see Team Arrow go up against a serial killer as the main villain of the season. Oliver finds out about Dover being the Star City Slayer and orders Captain Pike to investigate him to see if his family is involved. Pike befriends Dover while claiming to be Lawrence Tanner (the pedophile that Earth-1 Malcolm tried to get Thea to kill to help with her blood lust in the fourth season). After the Green Arrow foils one of his attempts to kill a boy, Dover begins to get suspicious of Pike and investigates him. After killing the real Lawrence Tanner in self defence, Dover realizes that Pike is actually the Vigilante before Oliver and the rest of Team Arrow discovers the truth about Pike.
Vigilante Unmasking: There are been big mystery that went unsolved in season 5, while fans suspected that Adrian Chase was the Vigilante, he was actually Prometheus. So exactly who is behind the mask of the Vigilante? I think that it might be Quentin Lance's replacement in the Star City Police Department Frank Pike (Adrian Holmes). I've always had a strange vibe whenever I saw Pike ever since the Vigilante first appeared. Pike is willing to break and even bend the rules sometimes to get results. In the flashbacks of season three, when Oliver killed a drug dealer at Tommy Merlyn's party, I noticed that Pike said it was community service after learning that the person murdered was a drug dealer or something like that. We also haven't seen Vigilante ever since Prometheus or Adrian Chase put Pike in a coma at the hospital. We actually never got to see Vigilante and Frank Pike together in the show too which is weird. It would explain how Vigilante has access to the weaponry he does. There's also another fan theory that Vigilante might have served at A.R.G.U.S under Amanda Waller or in the U.S Army under General Walker. I think Pike being an A.R.G.U.S agent would explain all the skills that Vigilante has as well as the training. I think that Stephen Amell did say in one of his tweets that Vigilante was one of the members in the Mayor's office.
More Thea Queen: I honestly would miss Thea Queen, it would be interesting to see how she would affected by Malcolm's death since he was family and was the last one she had other than Oliver. Thea would probably try to move on from Star City and go spend time with Roy Harper only to find that Roy now has a new love interest in his life who is Chesire or someone else. Maybe Roy's new love interest would have no knowledge of Roy's previous life since he had to change his name because of the events in the third season. I also thought we could introduce the Earth 3 version of Malcolm Merlyn who is the Green Arrow in his earth (It would be interesting to see that after seeing Malcolm impersonate Green Arrow in his fight against Damian Dhark in the mid-season four finale). Earth 3 Malcolm comes to Earth 1 after investigating a time portal on his earth and I wonder how Thea would react to meeting her father's doppelganger. Like Eobard95 says, Thea probably has shares at Merlyn Global Group which is why I can see turning into a business empire known as Queen Incorporated. I would honestly love to see Walter Steel come back as Thea's business advisor (like Lucius Fox), Felicity and Curtis coming to work at her company, and Thea competing against other entrepreneurs such as Ted Kord (if he's aloud to appear that is).
The Consequences of the Fifth Season Finale: There happens to be a fan theory about the season five finale where Slade was able to get Thea, Curtis, Nyssa, Diggle, Felicity, Rene, Lance, and Dinah away from the island in an A.R.G.U.S boat. However, Samantha Clayton ditched the crew to looking for her son William. Unfortunately, Samantha is one of the people who died as a result of the explosion caused by Adrian Chase. The others who died were Talia Al Ghul, the members of the cult led by Talia Al Ghul, and Evelyn Sharp. It would be interesting to see Oliver in his role as a parent as he takes in William as his own. I bet that William would be angry at everything that has happened and blame Oliver for it which makes him become a loose cannon for a while. Eventually, William starts to become more like the Gotham version of Bruce Wayne. Oliver would also have to live with Samantha dying and vow never to kill again.
Supergirl Crossover: I would love to see a crossover with Supergirl where Oliver meets James Olsen, who has become Guardian on his earth. I can see Oliver admiring James and taking him under his wing to train him. Maybe James might leave Earth 38 for a while to come join Team Arrow in Earth-1 for a bit to get the training he requires. I've always feel that Guardian needs to be trained by the Green Arrow whenever I see him in action.
More Deathstroke: I like to see more of Slade Wilson. Slade tries to look for his son Joe Wilson and meets him as well as a younger version of his other son Grant Wilson, the future Death Stroke from Legends of Tomorrow. It would interesting to see Grant's rise to villainy. Slade also tries to make amends for all the terrible things he has done by joining Task Force X or should I say the Suicide Squad just like in the comics. It would also be interesting to see Slade interact with the people his actions had a negative affect on such as Ray now that he's the Atom, Cisco now that he's a metahuman known as Vibe, and Caitlin now that she has better control over her powers instead of her other personality Killer Frost.
Black Siren's redemption: I was confused to learn that Earth-2 Laurel Lance would become a series regular in the sixth season. Maybe the best bet is to kill off Dinah Drake/Tina Boland/The Black Canary and have Earth-2 Laurel on the path of redemption. Malcolm later on became an anti-hero, Captain Cold and Heat Wave started to reform when they joined Rip Hunter's team, and Floyd Lawton AKA Dead Shot made a heroic sacrifice in season 3 when the Suicide Squad were against Joseph Cray.
Kill off 3rd Black Canary: As I previously mentioned, Dinah Drake needs to be killed off in order to have Earth-2 Laurel Lance on the path of redemption. I was thinkining that because of the Star City Slayer's presence in Star City, the FBI gets called over to investigate and they send one of their best agents Dorian Chase, the brother of Adrian Chase and another illegitimate son of Justin Claybourne. Unlike Adrian, Dorian disliked Justin Claybourne because of his corruption, but was sorry for his death after learning the Arrow killed him which is why he attended his funeral with Amanda Westfield. However, Dorian soon became glad that Justin died after learning how Justin was going to disown Adrian because of his psychiatric issues. Dinah at first has trouble trusting Dorian because of his brother, but soon starts to date him. However, Dorian and Dinah are both killed by Susan Williams, who is actually Dover's illegitimate child whom Dover tries to keep secret from his family. Dorian survives to become the second Vigilante after Pike while Dinah dies. I thought of making Susan Williams a villain similar to how they made Vicki Vale evil in the Batman telltale series and Adrian being Prometheus. Susan feels remorse for what she has done after learning how Dover never loved her. Oliver and Dorian decide to forgive her since Olivers feels responsible for what happened and since Dorian is nothing like his brother.
Team Arrow V.S The Bratva: I would also like to see Anatoly and the Bratva return as one of the main villains. The only reason that Anatoly returns is to go after the Star City Slayer since he feels that his presence is bad for his Star City branch. Oliver then gets upset upon learning that Anatoly is back and that leads to a conflict where the Bratva goes after Team Arrow while being led by Anatoly. Oliver and Anatoly's relationship would be a lot like Dexter and Isaak except that Anatoly could become the KG Beast. Or maybe it would be just Black Mask going after the Star City Slayer himself due to the same reasons as him being bad for business. Anatoly could come back after seeing his business in Star City being under the threat of Black Mask and that brings him into conflict with Oliver. They've introduced a lot of Batman villains in the show such as Huntress, Death Stroke, Ra's, Talia, Nyssa, and Anatoly, so why not Black Mask?
Less Flashbacks: Since we are no longer going to witness Oliver's flashbacks while he was away for five years, how about focusing on flashbacks that mostly apply to the story. Like there could be flashbacks about Diggle's time in the Army, Oliver doing stuff as the Arrow, and about other things.