The thing is what he wants. If he's getting drafted 2014 he may end up in a stronger environment as a potential 6-12th pick, where he getts less playing time and less freedom to operate. Plus he'll make more money long term, as he is another productive year of his career off his rookie contract.
If he decides it is college for a year, he'll have much time to address his weaknesses and get the right exposure in front of scouts to not end up being a sleeper pick. Plus 2015 from what I've read it's right now looking like Okafor followed by nobody. And he could enter the top3 easily and land on a rebuild team with freedom to do whatever he wants from day 1.
And then there's the option that he attends another Hoop summit or Eurocamp before the draft weighing 200+ lbs, having adressed his left hand and jumpshot. At this point it's getting really interesting in combination with strong draft workouts....I would not be surprised if he could actually attack players in the top5 or even top3 depending on circumstances like injuries, underperformance or just the prospect of Exum being a player that could play PG and SG at will. He'll obviously be a player who will be a playmaker in some way. If one GM thinks of him as an all around player like Brandon Roy without kneeproblems or an even better version of Ginobili, he might be on the rise.
But luckily and sadly that's 11 months from now and a lot of things will change in that time span.
If I understood Exum's situation correctly he's attending some boarding school for the best Australian Athletes and practices there with the best Australian Basketball prospects but doesn't really play in a tournament environment like a league?