I'm currently unable to submit an idea in this site so am starting by looking for feedback on how permissions currently operate in Canvas. 

We have a situation where multiple teachers are enrolled in the same course but specific teachers will grade some assignments in a course but not others.

We'd thus like teachers to only receive notifications in their To Do list for assignments that they will be involved in marking in that course. Instead, teachers receive To Do notifications for all assessments in the course, and there have been instances where some teachers have graded the wrong assignment.

While the simplest answer here is to ask the teachers to mark assignments complete that they are not involved with (or indeed using Act As to log in as each teacher and complete these for them), I was hoping for a more elegant solution.

So since Canvas is not currently designed to allow much control in limiting course content and actions for teachers, I was considering creating a custom role off the Student base role, and then giving this role as many of the permissions of the Teacher base role as possible. The hope here is that I could then use some of the restrictions available to student roles to control what assignments each teacher would see.

If this custom teacher role could be set up, possibilities here might include creating a section for each assignment, adding the relevant teacher to the relevant section, and then selecting that section in the Assign To field.
Or enabling Mastery Paths, creating a dummy assignment and using this assignment to define grade levels the teachers would need to reach in order to see an assignment.
Or adding each assignment to a separate module and then using module conditions to allow teachers access to the assessment that is relevant to them.

However, when I create a custom role off the Student base role, many of the teacher permissions can't be enabled for the role. When I asked Canvas Support about this, they advised that selecting teacher permissions off a custom student role like this was not possible.

My questions is, why are there restrictions as to what permissions can be selected in a custom role, and have others found ways to get around this limitation?

Thanks