Warren is the only guy I've seen pull off something like that. I don't know how he does it, but he frkn does it.
Here's the thing, if you're going to do it, do it with the right people. The last one I did was with Warren way back in March in Konoha. Make sure the people in the rp CARE about the rp and character development.
Since Warren's rp was the most recent one I did, I'll use that as an example. Some people who participated in it loved it because it provided opportunity for character development, a gm to control what's going on, the constant flow, etc.
Then there were others that frkn HATED/disliked it. Why? It's because they fell more into the 'zoner' crowd, or 'we just love to fight'. I don't know how he lived, but huge props to him to dealing with that.
Also, you have to deal with the time. Make sure you get people that post fast. In Warren's rp, that started in March. When did it end? I'm pretty sure it ended late May. Why? Because people were lazy and didn't post.
As the gm, which I presume you'll be, you'll have to be ON TOP of things. Like, you gotta be on top of people, read all their posts, etc., etc.. But if you get the right crowd, it should be fun.