I have been considering J1.5 for use by a ski club. It has three main sections each of which have several subsections and I have been in trouble with the present set up. As I understand this proposal it would meet my needs without modification.

At one point you indicate that your Use Case leads to a complex set of rules. You also comment that schools have complex structures and relationships. I have experience with nurse training organisations which I believe to be similar and would observe -

1. Many organisations or clubs are less complex - many much less complex.
2. With greater complexity come greater budgets and the chance of an administrator who understands those rules.

I think it is trivial to suggest - as would be the case for our club - that the registration form could include questions which would allow the applicant to self classify.

If some of our junior race trainees were going on a camp then a new group could be formed for that camp and registration to the camp could enter the individual into that group.

You suggested you would post the place to write short Use Cases but I did not see that.

This gets my vote and support.