There cannot be access to my block from within the Lesson itself.
"We have a very large user population so communicating that the block needs to be added to all users is not easy."
By "population", do you mean teachers or students? I suppose "teachers".
If I understand you correctly, you are worried that the operation of adding the "Lesson essays feedback" block is a separate operation from creating a new instance of the Lesson activity? And that teachers creating new Lessons might overlook the creation of that block? Thanks to the suggestion made by Michael Hughes in this post, the solution is to add that block at the time of creating a Lesson that contains at least one Essay question. Then, the block will be visible to the students after they have completed an essay question. If more than one Lesson instance contain essays, it is not necessary to add the "Lesson essays feedback" to all of those lessons, only to one of them. I encourage you to make the - small - hack to my block as suggested by Michael Hughes and to experiment. I will certainly make the hack myself in future releases of my block.
"Ideally there would be a 'Review previous attempts' link in the lesson activity itself, on an introductory page perhaps, to a complete report of each attempt such as the non student user as currently sees from the reports tab or a modification of that."
Yes, same as the Quiz's "Review attempt" feature. That would be quite useful, but would mean a very important programing work and there are no plans for it at the moment.