On the, "I've heard of this before." or "I've been doing this for... " Yes, it's called good teaching. In Finland, there's no grading or testing until learners take their university matriculation exams. Assessment is done entirely by teachers who give meaningful formative assessment and feedback to learners, no need for grades at all. However, it's a bit difficult to get that accepted by administrations that are fixated on quantitative statistics.
On the Quiz module suggestion and using the feedback comments, it only works for scores/right or wrong answers and that's the only way it can work. Computers cannot interpret learners' answers and so cannot judge why the learner got a question/task wrong, which is absolutely essential for providing effective, appropriate, meaningful instructional scaffolding. With this in mind, it's often a good idea to provide the answers to a question/task so that learners are more focused on how to get there rather than simply finding the right answers without understanding why.
Effective scaffolding still requires human interpretation and intervention, at least for the foreseeable future. On the other hand, some types of scaffolding, especially formative feedback, can be pre-written/pre-recorded (in a library of feedback snippets) and presented as and when a teacher/mediator decides it's appropriate (More able learners can provide scaffolding and feedback to their peers too!). In this kind of scenario, teachers/mediators can simply insert links to the relevant info or media. The Moodle Glossary module can be re-purposed for this quite effectively: http://blog.matbury.com/2012/03/01/using-moodle-for-written-corrective-feedback/ (Although, it'd be nice to be able to select and insert entries via a menu system).
The part that I think presents problems in Moodle is in recording the difference between what the learner can do unaided and what the learner can do with scaffolding (mediation from a teacher or peer). That's the learning potential (Tzuriel calls it cognitive modifiability) that dynamic assessment attempts to measure. AFAIK, Moodle's grade book doesn't record this explicitly but perhaps the grade history tables could be used for this in some way, i.e. a history of improvement in elapsed time and/or higher grades over several attempts. However, this doesn't show whether the learner was being aided or not.