That’s a difficult subject, but I try my best to give you my thoughts.
At first it sounds like a great idea. Writing FFs is a very big hobby for many people and to turn that into solid money would be awesome. If the people are contracted, it would also mean that the lengths and the quality of the FFs would have a certain standard.
On the other hand is there the risc of being screwed over as Bob Chipman said (I don’t know the guy, but he’s right). Plus how would the copyright issue be solved? FanFiction exists in a legal grey area. As long as we do not earn (professionally) money we can use the characters and stories of others but as soon as we earn money we could face legal issues.
And to be honest I don’t know if people would be willing to actually buy FanFiction. I certainly would be very reluctant to do so. If it was original work that would be a completly different thing, but fanfiction?
As an aspiring writer myself I wouldn’t be too fond of the idea that people make money off of characters and storylines I thought of.