I actually had a similar idea a few days back, except I wasn't thinking of Johan specifically. It was more of just "What if Shinji was a charismatic psychopath?"
There are, though, some interesting sociopathic sadists one could base the "new" Shinji on. Fore example: Hannibal Lecter (A good choice imo, as he's not without compassion. Brett Ratner called him "the huggy bear of serial killers").