That's not easy. I'll be honest about that. It's hard. I think that the solution is transparency. The option isn't like a regular stock option. There are a lot of things that must be included:

    1. Minimum and maximum hours per week that can be called-in. A person who intends on working full-time might set 0-12. (People can work over the maximum; there just isn't an expectation of top priority.) A person who intends on being a full-time consultant might set 20-50. 
    2. Industries for which a person refuses to work. 
    3. Willingness and ability to travel.
    4. How many of these contracts are outstanding. If someone wrote 5000 hours of options over the next year, that's patently ridiculous. There's no good definition of "too much", but buyers have the right to know. 
    5. Whether the person is working full time, and intends to continue doing so. 
    6. Priority resolution, as you mentioned.