There is a cognitive heuristic called the rule of seven that sort of states that it can be useful to chunk units so that there are around seven items being considered together at the same "level".
It'd be nice to use this in Org mode. Could I limit some (or perhaps all but a few) nodes so that they can only have 9 children?
org-lintto do the checking, which would not be hard to do I think. OTOH, it's not automatic: you'd kick it off and it would come back and complain about non-compliance.