Suggestion
A true "World Series". The ability to run a MLB, and pro leagues in Japan, Korea, Cuba, etc. and then have those league champs meet in a tournament to determine the true World champ.
Reason
We've taken the step of being able to run leagues in other countries. This is the logical next move. Let's see the Tokyo Giants face the Boston Red Sox for all the marbles, after having to eliminate teams from Havana and Santo Domingo, for instance.
Priority
Medium. Many of us would love it

, but I realize that it's not a critical addition.