Descriptive feedback is not new. This has been around for many years, as it has been shown to be an effective component of moving students forward, provided they make use of the feedback. For example, returning to a student a draft of an essay with suggestions (which can be delivered by peers or teacher). If the student chooses to ignore the time-consuming feedback, this will reflect their final mark on the essay. However, feedback does not take the place of final grades. I don't see why one must replace the other.