While quite a bit of research has been conducted on sex-change in reef fish, there are many discoveries left to be made and pathways to be elucidated.
The biggest mystery seems to be what biochemical component is responsible for instigating the changes observed. Thorough descriptions have been made of the process once it has begun, but few papers have dealt with what occurs in the fish to begin the process of change. The role of pheromones and other chemical signals also has yet to be invetigated.
It is my opinion that ultimately, the mechanism responsible for these changes is genetic, and it would be interesting to see the variation in sequence between the different strategies. From such information, it would be possible to produce a cladogram to put the different strategies into an evolutionary perspective.