As I see it, the grading system wouldn’t be particularly useful or beneficial 'cause, after all, it’d be based on personal subjective evaluations which, in a sense, it is already happening right now with the difference that it doesn’t gets reflected on a graphic or scale under the everyone’s eye.
Anyway, to add a suggestion on this topic, we could take the baton throwed by @bozoli and settle a categories’ system instead of grading people, that is, creating some “sections” to be rated by either volunteering community and users, like:
Therefore, we could get a general assessment about the work issued in each project or drama. That could generate a statistic algorithm in which, after a sum of good ratings (all calculated by the algorithm), the members involved would get a Status such as ‘Qualified Editor, Subber, Segmenter, Moderator’ (apart from the already in use contributor status). In order to do this, it’d be necessary to be able to assign the roles by the moderator (except this one pointed by de CM).
Antoher option, desregarding the aboves, could be limited to just take in account the general appraisal, figure out the team involved and draw our own conlusions for future recruitment.
However, I like better the Marketplace implementation proposal and also I’d rather leave the grading matter end up on the scrap heap of history.