Custom Overage Types and Units
Currently only two types of Overage Billing are available: Disk Space and Bandwidth, and both use the same unit: Gigabytes.
For our application we need to be able to add additional types and units. For example, one for us would be Processing Time, with a unit of hours. Another would be Number of Emails.
Right now this doesn't seem possible, but if it were, it would expand the range of products we could manage inside WHMCS.