Live action rights are different than animation rights.
And while I love Constantine and Matt Ryan I never really *got* Matt Ryan AS Constantine. I know its a minority opinion but he didn't really seem like Constantine to me. He clearly loved the role and has a ton of fans so I wouldn't be against his return though.
Side question: Why does Ray act like he's helpless since his suit was destroyed? Did he forget he lives on a time machine? He has access to any and everything he could possibly need for a new costume (not to mention access to all the sweet future tech). I'm sure I was supposed to feel something where he destroyed his suit but I just thought he would have a replacement by the end of the ep. Hopefully him as Jr Cold won't last long so they can deal with that.