Neat idea. I'd be particularly mindful to move in the direction of gaining mastery in an area, instead of gaining external rewards. We don't realize how often we condition our kids (and ourselves!) to buy into the carrot/stick methodology of motivating. There are isolated instances in which it works, but we pay a price. LOVE the idea of microcredentialing!
Self created goals, and a plan to meet them, is a good direction to head. I would suggest regular check-ins on the plan, some form of reflection, paired with formal feedback (peers?). The form, to me, seems stifling, but it would be easy enough to structure this so that it is open ended, allows for creativity and autonomy.
The sticking point, in my mind, is providing the extra time for teachers to get it done. If a teacher had one day off every two months to assess his/her progress toward a goal, if that teacher were afforded the whole day to delve into a meaningful reflection of his/her practice, if that day included one or two meetings with others who knew his/her goal and had a notion of his/her progress...then I imagine the teacher would follow through and make the process worth everyone's' while (especially the students'!).
Bill, I agree. Convincing organizations that hosting a shadow (or even an intern, as you suggest) would somehow add value to their bottom line is a major hurdle. My 9th and 10th graders are currently in the process of soliciting job shadow opportunities. They are discovering that this takes a somewhat sophisticated pitch, and that their pitch must address the "What's in it for me?" question.
It's possible that, over time, hosting organizations could receive a form of public recognition for their efforts. I also wonder if there may be some sort of "write off" available to them. There also may be situations in which expert teachers could help staff design training to "on board" new employees (teachers, theoretically, are experts in how people learn).
Overall, I think the effort to break down the walls that separate the world of business and the world of education will take a cultural shift, but shifts begin small. If we can convince organizations that they will be on the cutting edge of this shift it may provide some incentive.