Being the "big dog" in the martial arts world is what all these associations want to do. They are driven by "style" or "art", or whatever petty little thought process to try to gain control over other people and both their money and "progress". What has allowed MA to survive is the diversity of the situation, where you're free to choose where to train, what to train, and what level you have to be in order to progress.
Also, you don't just set up a "world governing body". It has to be authorized by somebody that's actually in charge legally of the outcomes, and responsible for the material passed on to students or competitors. It has tax consequences, legal restrictions, and obligations... which translates again into "money".
The idea has been around for centuries... take charge of everybody else's life, and only give them what you want them to have... I think Hitler, Stalin, and a few other people throughout history did that on another level... Sounds like the karate federation is already headed that way, so I can't figure out why we need another group doing the same thing?
Rank is the honorary standard of the people you train with... so under your "governing body", a guy in Indonesia or Thailand is going to be able to set the standard for Korean TKD or European Shotokan?... I don't think so...
It's a grand design... and had MA developed in a manner and way that accommodated it, it might have worked "early on", but simply "assuming power" over something like MA wouldn't be as easy as you think. In some countries, the governments are the "governing body" for MA... so you'd have to also be a U.N. member to make it work...
Send me my requirements... I'll try to live up to them...