Given the amount of experience you've had running other online leagues, I'd say "what are you waiting for?"
I don't have any real evidence to support this statement, but I think the problem is not that there aren't enough potential GMs, instead there aren't enough quality on-line leagues around.
I'm always on the hunt for one more league to join, but I've noticed that the good ones not only have no vacancies, they have a waiting list.
See
Online Leagues - What do you like/dislike? where I've already put my own likes; I'm surprised more people haven't responded.
cheers