At this very moment Halo 4, in my opinion, is not competitive at all. There are WAY too many "cheesy" tactics that can be used which, although very effective, would diminish the fun aspect if everyone used it. Imagine a game where everyone decides to use Camo while hiding with a Boltshot or Shotgun.
There are also no real competitive game modes. At the moment the only numerical value we place importance on is our KDA ratio which isn't even publicly displayed. In order for Halo 4 to be taken seriously as a competitive game (maybe even e-sport level) would be to add some sort of visible ranking system. In LoL (a completely different type of game, I know) there was Elo which was visible to everyone. Only the game mode called "ranked" would be able to bring your elo up or down while all others would only change your invisible Elo that's only used in matchmaking.
This link does a much better job at explaining elo than I ever could:
I firmly believe that once a strong competitive game type is introduced for normal players that eventually we will have plenty of pro teams that could compete on a global scale. I would LOVE to see a strong e-sports presence for Halo. I just started playing it but I already love it. I would love to see it grow on a competitive level.
The financial benefits are huge, too, if Halo grows as an e-sport. Not only can 343 make money off of tournaments, but streamers could making a living off of their streams. Top Halo 4 streams have only a few hundred viewers while top LoL streams have thousands. That's a lot of money!