So I've been thinking about my ARG compilation project (mostly how the heck am I supposed to structure this thing), and something dawned on me - you can only really do an ARG with some sort of subversive storyline or underground movement. It invites players to follow the story since they're doing something they shouldn't be doing.
In A.I. it was solving a murder that had been covered up. In Year Zero it was discovering a government conspiracy. In The International, it was discovering a conspiracy involving banks. And in TDK, it was being part of the Joker's gang and being privy to the mob corruption.
So I guess if The Riddler (or whatever villain it is) isn't up for having a large group of followers, Citizens For Batman could continue their quest to figure out their namesake - what has he been up to, did he really kill those people, etc etc. But it probably won't be as easy as that.

Just something to think about.