Film directors such as Bryan Singer need to be working for some sort of agency that has a pool of directors in its employ. It would be the job of this agency to decide what project their directors get assigned to based upon their availability.
For example, NBC-Universal would call up this agency and ask which of its directors are presently available to begin working on their "Munsters" reboot project. This agency would know moment to moment what projects their directors are working on, and how long it would take each of their directors to finish the projects they are on.
At the risk of sounding unprecedented, it would be the agency (and not Bryan Singer for example) that would decide what his next project would be based upon the needs of their clients (the movie studios) calling with their film director needs. This agency would also, never...ever...assign more than one project to its film directors at one time. The agency would assign one project and one project only to each of its individual film directors with the full understanding that once the project is assigned, that director would be devoting his / her full attention to that one project (and nothing else) for the next 18 months or however it long it takes that film director to direct and film that movie.
Because I gotta tell ya'...I gotta' tell ya'...Bryan Singer has been all over the map with conflicting and overlapping potential directorial assignments crushing his work load with enough work to fan out to a dozen or more film directors at one time. This in itself is an argument against film directors being independent contractors (their own bosses.) At the risk of sounding unprecedented, Bryan Singer needs a corporate boss (not an agent) to assign directorial assignments to him one movie at a time. And he wouldn't get another movie assignment until the previous assignment is completed. This would bring some organization to Bryan Singer's professional life. It would also remedy the all too frequent problem in Bryan Singer's career of multiple potential film projects overlapping onto his schedule at one time:
1. Six Billion Dollar Man
2. Battlestar Galactica
5. Jack The Giant Peach
6. X-Men 4
7. X-Men 5
In short, Bryan Singer needs to be thrown into a pool of film directors all working for this agency, and he would get a mandatory directing assignment as long as he completed his previous, mandatory directing assignment.