As far as I know, John is a paranormal detective. He usually works alone, but sometimes he gets the help of those involved in the war of the heavens. I like him, because he says a fuck you to both sides. I would love to see him in the game, too.
I agree that it would be hard to have him in the game as he is not really someone that goes into combat... they thing is this guy has changed so much. You go to remember that his is a creation of Alan Moore and then rocked to fame from Hellblazer which was published at Vertigo (a dc inprint designed for adult comics).
What I am getting at here is tat he is a complex character that was written for nearly 20 years in a adult comic full of ultra violence, sex, horror elements and other adult themes. Specifically written I might add as a "non-super hero comic". I mean he hardly even uses magic and kinda sucks at it anyway.. he is more a con-man grifter kind of bloke.
Though he was so popular that he has worked his way into main stream DC and what many people consider him, is not what he is written as any more. I mean nowadays he is throwing around fireball spells like some lame d&d larper and stuff. Fighting super villians and there was this TV show where he was some kind of detective.. wtf....
When he was just a total lowl life arsehole con-man scumbag originally. The kind of guy to light his cigarette on your flaming body then use a fire extinguisher on you. Lobo has gone through a similar thing... Those characters are so popular DC "wants" to use them, but Constentine is so complex a character thanks to Allen Moore and such a scumbag that they had to tone him down.. just as Lobo no longer eats babies and casually murders entire planets of people just for kicks.
I guess what I am getting at here is that he has changed so much I barley recognise him anyway.. having him kickbox and throw spells about wouldn't be a stretch for his new direction. I mean did you see the Justice League Dark animated film? That version of him could totally be in Injustice 2.
but whatevs
