According to the updated FAQ on the MGSV site, there are plans for official tournaments for Metal Gear Online. These will be announced in the future.
The FAQ also confirms that Metal Gear Online will allow you to play with players from all over the world. Earlier, the team said that there are plans to make the game region free, and now it seems to be official. The Japanese FAQ mentions that players will be able to choose between ‘Japan’ and “ROW’ (rest of world), but this isn’t explicitly stated in the English FAQ so perhaps the menu will work a bit differently.
Source: MGSV FAQ, via MGOForums