The agreement with the Union is max 2 years on "leave of absence".
Current bunch of "Core FO's" on LOA will have used 12mths of their 24 mths basket after they spend some time up North on temporary core Command this Summer.
Therefore, I doubt if anyone can reliably answer what the future will bring until Summer 2015 . . . . finally NAS need Capts in left seat (not right) so no doubt some "acommodation" will be negotiated.
We have Core FO's who have been on "Temporary Command" - in core bases, NOT as Contractors (usually for 6mths at a time) for 4 years or more, so . . . . . . NAS do wish to use you as a Commander .