Well. GM managed or not, it can be player hosted in all simplicity.
A GM would only be really required if you only want it recorded somehow, or to enforce rules.
However, there really wouldn't be many rules...
I mean, really. Why would you really need a GM?
It'd kind of just be a way to gloat about who's the best,
or a way for more free tickets to those who are already rich.
I don't remember, but I think I suggested something like this a long time ago.
Something about limited items, like you get 20 points to spend and each item including equips is a point.
Or something, then the GM's would de-buff you and take you somwhere in a 3 man team.
Then they'd check your items and equips, etc. Sort of a neat tournament.
Rejected though. I think.
Either way, this would totally be optional. But has been done. Nothing new.