Well as much as I like to bash soccer, I find it excessively boring, and the culture that surrounds it causes me to just roll my eyes, I don't think this WI could be pulled off. The utter simplicity of the game means it was inevitable that it would become the 'world game'. At it's most basic, you're running around chasing a ball, a fun little game that kids naturally play anyway.
Now a more interesting WI would be to replace soccer now. We live in a world that is more prosperous, a world that has access to and influenced by many different cultures. What sport could conceivably replace soccer now?
My top three: hockey, Canadian football, and curling are out. Hockey is my favourite, but it is the most equipment intensive and building intensive sport, especially for those that live in warm climates. The same for curling which requires less equipment but still needs a specialized enviroment to able to play. Canadian football would need the Americans to suddenly adopt Canadian rules and field size. That's not going to happen.
Realistically baseball and basketball are the only two that have a shot at it. Both are fairly simple at it's heart, doesn't require special enviroments. Can be played year round in warm climates. I like baseball, not a fan of basketball, so I know which one I rather root for...