Sinestro made his first live-action appearance on "Green Lantern" in 2011. He is a great villain and he fits very well to Green Lantern. It would be very cool to see his origins and the way he turns evil.
Eobard Thawne aka Reverse Flash/Professor Zoom
We've seen already Thawne on The Flash and I think that Tom Cavanagh portrayed the villain really good. Zoom is a great villain I think that he should be in DCCU's The Flash movie.
Jason Todd/Red Hood
I never thought Red Hood as a villain in the story, he's more of an anti-hero to me. Jason's story is the best story for me. We've already got a glimpse on Robin's suit on Batman v Superman: Dawn of Justice, but we don't know what really happened. I bet is Jason suit and as I said in the previous article about Jason being the Joker, I don't really believe that.
We've seen Jason as Red Hood in Batman: Under the Red Hood, an animated movie that every fan should watch.
Also we've seen Jason Todd as the Arkham Knight in the game Batman: Arkham Knight which he turns to Red Hood.
Ra's al Ghul
We've seen in Ra's in Christopher Nolan's The Dark Knight Trilogy portrayed by Liam Neeson and at my opinion it was really good.
First reason that he needs to be in DCCU is because he is the one that brought Jason to life after the Joker murdered him.
Secondly, he is a great villain and antagonist to Batman and we also have to see a war beteween Batman and the League of Assassins.
Slade Wilson aka Deathstroke
We've seen Slade on Arrow and the story they made for him is awesome, I think we should see him again. Also I think that he has to be on DCCU you, he is a really good character and antagonist to Batman.
I think that we have to see his real origins from the comics because he is a unique character which we have to see without discussion.