I maintaining the web services in Moodle. I've happily discovered from the dev meeting this morning that you are planning to implement some web service functions. What are your advancement about it? For info, I've just read http://docs.moodle.org/dev/Assignment_Web_Services.
As you most likely know, the lightwork team is working on some web service function specs related to assignments:
MDL-31683 - core_course_get_courses_and_assignments
MDL-31681 - core_grade_get_rubric_grading_definitions
MDL-31274 - mod_assignment_get_assignment_submissions
Once an issue specification is validated, I add the the issue to the roadmap MDL-29934.
It seems like your are planning to write some similar functions. (PS: I don't know how much contact you have with lightwork team at the moment)
To help me to organise all the work about web service, I would suggest this workflow:
1- check the lightwork issues + the ones in the roadmap MDL-29934. Then participate on each function issue you need so we have end up to clear specification.
2- create one issue by missing web service functions in the tracker.
3- I guess you can keep
MDL-31273 for personal purpose to follow up if all you need gets integrated in the roadmap issue. It's as you prefer for this one.
Let me know if it's ok for you.