Currently there are sort of 3 levels of Administrative access: 1) Full Administrator, 2) Group Administrator, and 3) Non-Administrator.
Consolidating these settings into one place and adding a fixed set of controls would allow for better per-user modification of privileges. For example, if the per-user drop down that currently sets Full Administrator or not were expanded to be Full Administrator, Limited Administrator, or Non-Administrator, an additional page could be added to control accesses for those marked as Limited Administrator. This would add controls for specifically targeted things like Subscriptions and Canceling Reviews (list could be expanded over time). Additionally the Group Administrator settings could be moved/mirrored here so Group Administrators could be added from their user accounts rather than only from each individual Group setting. Things like Canceling Reviews you're a member of the Group Administrators for could easily be controlled from there on a per-user basis.