Except to make it the biggest of all time you would add MMA fans and kickboxing plus even Asian especially Chinese styles to draw those multi millions.
if one had a time machine all you would need would be one fight: ALI vs. TYSON. it would be a bigger event than the birth of jesus.
Can you mix the 2 sports? The biggest event would be something like this Wlad vs Whoever the UFC heavyweight champion is Floyd vs whoever their champ at a comparable weight is Pac vs their champ from a comparable weight Do those 3 fights and the rest of the card doesn't matter. But you'd be smart to throw in an asian fighter and a euro fighter. Bill it as boxing vs MMA and it would sell millions