First, we have to understand from the contributors point of view. There are basically two groups of contributors. Those that make thousands of dollars every month, and those who make pennies.
The Successful earn 50% from Shutterstock and 50% across all other agencies.
The Failure earn 95% from Shutterstock and 5% across all other agencies.
The above is however, a hard fact. If Shutterstock offers exclusivity, the Failure will immediately join the offer without doubt. The Successful, on the other side, will dangle between the fence because it is such a risk for them to change what is already successful.
In the end, Shutterstock will build up a lot of EXCLUSIVE, BUT LOW QUALITY images/vectors. This will not only harm Shutterstock, but the big contributors as well. The only winner here is the Failure which fail to produce quantity and quality.
To comprehend more, exclusivity means higher pricing, ranking, and royalty percentage for contributors. So, if the majority of the exclusive contributors are the Failures, you can imagine how poor Shutterstock will become. We cannot compare Shutterstock and IStockPhoto here because IStockPhoto has the first-mover-advantage in the industry. IStockPhoto captured and forged the Successful one when they have yet to become successful.
Unless Shutterstock can offer a very delicious and lucrative exclusive offer, then it might have a chance to totally win the heart of the Successful contributors, and at the same time, eliminates all its competitors once and for all.