I think, though, that as long as the teacher retains the final say each effort to get past the grading barrier is going to be crippled to some extent. As long as teachers reserve that right, contracts and any other attempts to reconfigure authority can be undercut and even be disingenuous. I think if we're going to share authority with students it's got to be authority and really shared. What this means is, we negotiate grades with students as colleagues. We give up our veto power.
Damn thing is more of a burden than a boon anyways.
I don't see this as abdication of responsibility or as an easy way out. Because the grading burden is so firmly placed on teachers, it takes considerable effort to move it and redistribute that authority. Of course, negotiating is never easier than laying down the law. Relying on rhetoric forces us to use our skills rather than our authority, but in the process, we may become better examples for our students to follow. The best situation would be to enact something like real world evaluation, a system of peer and community assessment of work.