Stupid idea because you would not be to find 16 fighters from 16 countries on anything remotely resembling the same level.
You ever heard of a Spanish MMA fighter? Or an Italian one? Or maybe a badass Czech MMA fighter.
If you were to chose fighters based on their abilities, one third would be Brits, one third Poles and one third Dutch kickboxers.
Since Ronda can beat Cain and Mayweather, can Holly beat Cain and JDS at the same time? Or Mayweather and Pacquaio at the same time?