With only the top illest spitters ever with no rules except that they must spit the illest they can. They could spit at whatever pace however they like as long as the bars are nothing but fire. The song could have like..
Crooked I, Chino XL, R.A. The Rugged Man.Eminem,Brotha Lynch Hung, Andre 3000,z-ro,
Of course there would be far more than that but thats all I can think of right now..
And they could go by country/region so the styles could flow smoothly together and to make room for more they could just tell them to at least ride the beat and not pause much.