thanks a lot for this review. It really provides a valuable feedback.
I want kids to be able to assess using a rubric and give written comments as well
Yes, this is to be added for the next versions of Workshop - a field for overall reviewer's comment. You may wish to create a feature request in the tracker so that it does get lost.
Once you go into the Assessment Phase it is tricky to go back
Is it? I am not aware of any "heaps of problem" with reverse phase switching. Can you please elaborate?
It seems to be impossible to easily get in and remove or edit a student assessment that is clearly way off the mark
Let me disagree. This can be actually done pretty easily by lowering the weight of such assessment. If you set the weight of an assessment to zero, it does not influence the submission's grade at all. Of course that the teacher can not edit the assessments. But they have several ways how to influence the grades calculations. See the Workshop docs page for details.
Navigating the results page is difficult
The table with results can look complicated for the first sight. However once you realize its logic and get used to it a bit, it provides many useful information. You are welcome to suggest improvements though, of course!
Grading is not anonymous to the students and it should be
Let me disagree again. The peer assessment process can be fully anonymous. It is just not set in the Workshop edit form but via overriding capabilities. There are two capabilities that control the anonymity of reviewers and reviewees.
Thanks for the link to the peer assignment plugin. It was considered during the initial workshop 2.0 design phase.